Installing a Composting Toilet
In 2008 the toilet in Sarah's head was showing a lot of age and needed either to be replaced or a major overhaul.  Also the LectraSan sewage treatment system was about to give up the ghost and it was not even legal in many areas of the US.  So a holding tank was probably going to be required, something that would be difficult to fit on Sarah and a lot more plumbing.  After having to clear a sewage hose on the way from Bermuda back to the Chesapeake Bay in 2007 I started looking for alternative to the standard seawater flushed marine toilet. 
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The Airhead Composting Toilet
The only real alternative is a composting head - one that does not discharge sewage, but rather allows it to compost onboard turning it into fertilizer.  I heard of this type of head for years, but the concept seemed a bit extreme.  However as the concept of a discharging head became more and more undesirable, the alternative began to appear much more acceptable.  Practical Sailor had done a review of several composting heads back in 2002, and they concluded that it was a workable solution for a marine toilet.  I also heard from several live-aboards who installed composting heads on their boats and were very satisfied with the arrangement.
At the time I was only aware for one brand, the Airhead (shown in these pictures), from the Practical Sailor article, the live-aboards, and boat shows.  So in 2008 I purchased the Airhead and began planning the installation.  Subsequently I learned of another brand, Nature's Head, which also would be a good solution for Sarah's Head. Click on picture to view at full resolution
The Airhead Composting Toilet
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The Airhead Composting Toilet
The base of the toilet is the composting chamber.  The toilet bowl detaches from the base and the base can be removed from head to dispose of the compost periodically.  Live-aboard couples claim they can go up to six weeks without having empty the chamber.  The other chamber protruding from the base is the urine bottle.  The secret to composting is to control the moisture in the composting chamber.  If urine were added to the chamber the compost process would take much longer (until the urine evaporates) and probably would produce unpleasant odors in the head.
This is the business end of the Airhead.  In the interest of good taste I've taken these pictures before the Airhead was installed and before it was ever used in anger. Click on picture to view at full resolution
The Airhead Bowl, Trap Door Closed
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Airhead Bowl, Trap Door Open
In this picture the trap door to the compost chamber is open.  That is all there is to flushing this toilet - allowing the waste to drop into the chamber.  The manufacturer recommends using Mr. Coffee-style coffee filters to catch the waste before the trap door is opened, but several users claim they no longer use the filters, but just drop their business directly into the chamber.
Maybe this is more information than you really want.
The two holes in the toilet bowl, forward of the trap door are used to collect urine.  Yes, this is a gender-equalizing toilet.  No one gets to pee standing up in Sarah's head after this toilet is installed.
The Airhead uses a standard compact marine toilet seat - the same as on the Raritan PH-II head that came with Sarah.  One difference is that the Airhead provides gasket seals on the bottom of the seat and the lid to contain any odor.
One of the advantages of the Nature's Head composting toilet is that it has a standard household toilet seat molded into the unit.  Since my butt is definitely not a compact size the full-sized seat might be a significant advantage. 
Still I've managed to get my business done on a compact seat for the nearly 5 years of living onboard, so I guess I can continue to get my business done on the Airhead.
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Gasket Seals Under the Toilet Seat and Lid
The major installation task (other than removing all the old plumbing) is the installation of the vent which brings air into the composting chamber.  I wanted the vent hose to be out of the way on Sarah and not take up a lot of valuable space in the small head.  The ideal spot is in the little alcove just outboard of the companionway stairs that are on the opposite side of the forward bulkhead.
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Liner Removed from the Head
So first I removed the headliner. This involved removing a lot of molding and trim pieces.  Even then the headliner resisted coming out.  Clearly the headliner had never been removed from the head since Sarah was built.
The headliner did finally come free and I could see the underside of the trunk cabin where I intended to place the vent.  There is a 1/2"x4" piece of wood glassed into the corner of the trunk cabin to provide stiffening.  The 3-1/2" hole for the vent would have to partially cut into this stiffener.  That meant I would need to fit some cleat stock inboard of this to provide a flat surface to attach the vent fan. Click on picture to view at full resolution
Location for the Vent
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Cutout From the Coach Roof
The first task was to cut the hole in the trunk cabin with a 3-1/2" hole saw.  The edge of the cut-out is shown in the picture on the left.  The trunk cabin is about 1-1/2" thick with a 3/8" outer skin of fiberglass and a 1/4" inner skin with 1" of balsa completing the sandwich.
On the right is the hole in the deck with the cleat stock installed.  Notice the air gap between the cleat stock and the coach roof stiffener.  This was an installation error that I had to correct a few years later. Click on picture to view at full resolution
Hole for Vent and Cleat Stock Air Gap
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Vent for Airhead in Place
On the left and below is the deck vent fitted next to the companionway hatch.
This is a passive 3"  Nicro vent.  Click on picture to view at full resolution
Nicro Vent
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The Airhead Fan Housing
In this picture the headliner has been re-installed and the vent fan housing installed under the new opening in the coach roof.
I cut this corner of the headliner off from the main piece.  This made it easier to cut the hole in the headliner for the vent opening, but it will also allow me to remove the main part of the headliner in the future without disturbing this vent for the toilet.
The fan housing is secured by screws that go through the headliner, through the cleat stock, into the coach roof.  This housing must support the weight of about 6' of 1-1/2" vent hose, so I want it to be very secure.
Now all I have to do is hook the fan up to a 12 VDC supply and I can remove the old PHII toilet and install the Airhead.
This is a picture of the vent opening in the coach roof with the Nicro vent removed.  The vent fan is visible.
Yes, I know I really chewed up the coach roof gel coat with the hole saw.   I drill one of these holes about every 5 years and I always forget that when using a large hole saw in hard material you have to run it in reverse, at least until you get through the outer fiberglass shell.  I am starting to believe I have forgotten more things than I ever knew.  Getting old is a bitch.

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The Vent Fan
The picture above also exposes a major mistake I made in the vent installation.  There are air gaps between the glassed-in plywood trunk cabin stiffener and the cleat stock I added.  This allows some of the air coming from the compost bin to escape into the area between the headliner and the trunk cabin roof.  When Steve Angst and I were taking Sarah south in the fall of 2008 we noticed there was some odor in the main cabin, but none in the head.  I couldn't figure out how that could be as the hatches were closed and the wind was blowing over the bow and should have pushed any odors aft, not down in the cabin.  When I was updating this page I noticed the gap in this picture and suddenly realized how those odors got into the cabin.  That was also a time when I was still experimenting with how much COIR to add to the bin.  With sufficient COIR there are no odors, and this gap is not a major problem, but it needs to be fixed.  I will probably use some rope caulk to fill the gaps.
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Added Butternut Trim to Cover Wallpaper Gap
While I was messing with the headliner and trim pieces I decided to finish covering the places where the wall paper had been removed during the bulkhead replacement.  I found some of the Butternut stock I had used for trim around the bulkhead.  I used that wood to cover the gaps in the wallpaper.  I still have to shape the pieces a bit and then varnish them to match the other Butternut trim in the head.  They will not match the original teak trim pieces, but I will not add anymore teak to Sarah' interior or exterior.
Finally on May 30 I removed the Raritan PHII toilet from the head.  I also remove the pedestal on which the toilet was installed.  You can see the outline of the pedestal around the large hole in the floor of the head through which the seawater intake and seawater outtake hoses were run.
Old Toilet and Pedestal Removed from Head

Hole for Removed Sewage and Water Hoses
This hole is in a platform above the cabin sole on which the toilet pedestal was secured to mahogany cleat stock.  Removing the cleat stock turned out to be the most difficult part of the de-install.  Removing the counter-sunk wood screws required a lot of pressure a Philips-head screw driver with the added leverage of a vice-locks wrench.  The final two screws had to be drilled out.
In the picture on the right I have placed the Airhead in what I expect will be its final location.  I decided to wait over night before  securing it to this position and then cutting the vent hose to length.
Airhead Toilet in Place

Toilet Secured and Vent Hose Attached
The next day I secured the brackets that hold the toilet in place to the toilet platform.  I then cut the vent hose to length and attached it to the toilet bowl.
Now the installation is basically complete.  The big (and unpleasant) job that remains is to remove all of the water and sewage hoses from Sarah along with the LectraSan.  This will be a messy and complicated job.  To remove the LectraSan I will need to remove all of the water pumps (frig, A/C, shower) that currently reside just aft of the LectraSan.  While I'm at it I will remove the low-volume seawater manifold and clean it up.
I am a little concerned that these SS brackets will be strong enough to withstand the sideways force of someone (me at 250 lbs) sitting on the toilet when the boat is heeled or rolling.  Other users have not reported problems in this area, which is why this is only a small concern.
Bracket to Secure Airhead

Peat Moss Brick
So now the Airhead is operational.  The brick of peat and the enzyme package are on the counter, ready for the first use of the toilet.  Since I'm a regular guy, that should happen tomorrow morning.
Don't expect to see a report on how it went posted on this website.
 No need to avert your eyes from this picture.  That is just the crumbled up peat moss in the base of the toilet. 
This is not the correct way to use Peat Moss as I would learn later.  It should be re-hydrated before being put in the bin.

Peat Moss in Compost Bin
Learning To Live With Peat
Well, once again I failed to carefully read and follow instructions.  As seen above I just crumbled the peat brick and placed it in the composting chamber before my first use of the toilet.  The instructions clearly state that the peat must be moisturized before putting it in the toilet.
Without the moisture the peat does nothing to desiccate the waste, aid the composting and absorb the odors.  After a few days of use the head had a very strong odor.  The odor wasn't unbearable, but I had been told by the manufacturer and other users there is almost no odor from the toilet.  I had expected only a very slight odor of peat.  This definitely was not a slight odor and it definitely was not a peat odor, so something clearly was not working right.

Re-Hydrated Peat Moss
After an exchange of emails with the manufacturer and re-reading the instructions I realized my error.  I tried adding water to the composting chamber, but that did not seem to help much.  I finally found a local source for the Sphagnum Peat bricks and I hydrated the brick in a Zip-Loc bag as shown in the picture on the left.   This brick is only partially hydrated because it would expand beyond to capacity of the 1 gallon bag if fully hydrated.
I've subsequently found that very large Zip-Loc bags will hold more than the contents of one hydrated brick of Peat Moss or COIR.

So I just added a few handfuls of peat to the composting chamber and within minutes the odor had greatly diminished.  By the next day the odor was completely gone.  I will keep adding water to this bag adding more peat to the toilet until the entire brick is in the chamber.
It took me a few days to find a local source of the peat.  The garden section in Wal-Mart, Lowe's and various hardware stores in my area do not carry these bricks.  They do sell loose Peat Moss, but the smallest bag is 22 liters.  I found a larger gardening/nursery supplies store, but when I asked for Cocoa Peat they couldn't find it in their catalogues.  That's because I was using the wrong name.  What I should have been asking for is COIR, which is dehydrated Coconut Husks, not Cocoa.  Browsing the store I found a brick of Sphagnum, which from Wikipedia I knew was Peat Moss.  It was the only brick they had in the store.
After discovering how to use the brick and determining that it takes care of the odors, I used the Internet to find another source for this material.  Through that research I learned several things.

  1. Sphagnum Peat is largely a non renewable product.  Although there are several sources that harvest the product in a manner to not destroy the bogs in which the peat grows, much of the product is just ripped out of the bogs and not replaced.
  2. The alternative to Sphagnum is COIR, which is the Coconut product that I was originally looking for.  It is made from the dehydrated husks of coconuts and is a renewable source since only the fruit of the palm tree is harvested not the entire plant as is the case with Sphagnum.
So I've ordered several bricks of COIR from a gardening website ( and will use that peat in the future.
Emptying the Airhead and Converting to COIR
After nearly 10 weeks of live aboard use I finally emptied the composting chamber, and this time recharged it with COIR instead of Sphagnum.
10 weeks seems to be pretty consistent with other live aboards' experiences.  Several couples have reported they average a little less than 6 weeks to fill the chamber.  I am the only user of my Airhead.
I probably could have gotten a couple of more weeks of use if I didn't have those large chunks of un-moisturized Sphagnum in the chamber because of my initial screw-up described above.
For the re-charge I had several bricks of COIR on hand.  I'm still working my way through the logistics of handling the compost material, and I am still making mistakes.  Prior to emptying the compost chamber I placed one of the bricks in a 1 gallon Zip-Loc and added a couple of cups of water.  This caused the COIR to expand to the limits of the Zip-Loc and I could not moisturize all of it.  I took handfuls of the moisturized material and placed it in the emptied chamber.  This was a little messy as it is difficult to hold the crumbly material in one's hand without letting lots of little pieces sprinkle about the head compartment.  I also was not able to place enough material in the chamber for satisfactory use.  I was having to moisturize the COIR a little at a time.  So after a couple of uses the COIR in the chamber was over-whelmed and I was getting an unpleasant odor out of the vent.  In a few days I got all of the material from a single COIR brick into the chamber and the odor disappeared.

I've revised my method for preparing the COIR.  I placed another brick in a dry-wall-type bucket and added about 1/2 gallon of water.  The COIR absorbed the moisture within a few hours and expanded to about 2 gallons in volume.  I then placed the moisturized material in two 1 gallon Zip-Loc bags (shown in the picture on the right.  Now I have a full brick of material ready to add to the chamber on the next re-charge.  I also have material to add if more COIR is required on the current tank cycle.

Hydrated COIR and COIR Bricks
My initial impression of on the use of COIR in place of Sphagnum is fairly neutral.  COIR seems to work as well as Sphagnum, but it is a little more messy to handle.  Unless there is a problem with the current cycle I'll stay with COIR.  Also shown in the picture are two spare bricks of COIR that I purchased from Gardner's Supply (link above).
Emptying the Urine Bottle
Much more frequently than the compost bin, the Urine Bottle must be emptied.  While dumping the bottle overboard does not pollute (Urine is sterile - no bacteria) it is generally not something other people like to observe.  It is also illegal in the U.S.A.  I suspect dumping urine was made illegal to take away the claim of a person caught with an overboard discharging toilet, that they only pump urine overboard.
When at a marina I could take the bottle into the toilets and pour it down a commode or urinal.  However that is often a long trek and won't be greeted any more enthusiastically by other persons in the toilets than the folks having cocktails in the cockpit of the boat in the next slip.

Urine Bottle Gauge
So my normal procedure is to check the urine level (gauge shown in the picture on the left) each evening, after dark before going to bed.  If the bottle is more than 75% full I dump it overboard.
Unfortunately the gauge, which is just vinyl hose, has become stained such that it is difficult to read the gauge. On more than one occasion I have checked the urine level before going to bed and decided it did not need to be dumped.  The next morning I discovered that in fact the bottle was completely full.   Now it's daylight and dumping the bottle overboard is a problem.  I have a spare urine bottle for those incidents. 
It is very important to prevent the bottle from filling to the top.  I let that happen just once.  It is non-habit forming.
Recently (Dec, 2008) I spent a month in a Florida marina where my boat was located in front of a popular bar/restaurant.  My boat was illuminated by the lights from the bar and the marina.  This made peeing off the deck or dock a very public event until well after midnight.  It had also turned cold early in Florida and peeing off the deck at 3:00AM wasn't all that appealing even without the audience.  So for nearly a month I was using the Airhead for almost every pee.  I discovered that by myself, I could fill the bottle in less than 4 days.  So, then I didn't really need the gauge, I just emptied the bottle every third night.
FWIW, the urine level in the picture above is just barely on the bottom of the gauge.
After One Year (2009)
Well, I've been using the Airhead for over a year now.  That included over 4 months anchored in the Bahamas with no choice of using a marina facility.  Even when I've been berthed in a marina I've normally used the on board toilet, both because it is more convenient and to fully exercise the toilet and find any limitations.
Overall I'm very satisfied with the decision to go with a composting toilet in general and the Airhead in particular.  There really haven't been any serious gotcha's.  Oh, I've let the urine bottle overflow once or twice and my experimentation with how much COIR to use still goes on, but it has really worked as advertised.  Even my friend Steve Angst who crewed for me on the way to the Bahamas last year and for a week in the Abacos felt it was a good choice.
There are several things I've learned in this year.

  • Always have a spare urine bottle on board.  Without a functional (i.e., non-leaking) urine bottle the toilet is nearly non-operational.  I purchased a spare before heading for the Bahamas.  My fear was having to empty the bottle at sea and then dropping it overboard and watching it sink to the bottom of the ocean.  Turns out the bottle can fail.  The original bottle started to leak around the bottom sight tube fitting.  It took awhile to figure where it was leaking in the mean time the toilet remained operational with the spare bottle in use.  It looks like the elbow fitting has cracked.  I contacted Geoff at Airhead and he said there had been problems with the elbow fittings cracking the threads molded into the bottle.  I confirmed that the threads in the bottle wall were cracked (picture on the right), and he said the fix would be covered by the warranty.  I received a replacement bottle within a week.
    One other reason to have a spare Urine bottle is to always have an empty bottle available when the one in use becomes full.  This eliminates the need to immediately empty the bottle when full.   This could be an inconvenience in a marina or a serious problem when underway in rough weather.  The bottles have screw-on caps that seal the bottle and prevent spillage until it can be emptied.  Additionally switching to a spare bottle minimizes the time the interior of the toilet is open to flying insects (see next lesson learned).
  • Gnats!  I did develop a large colony of gnats in the compost bin upon return from the Bahamas.  The Gnats probably came on board because I was once more putting wet refuse in the garbage bin in the galley.  While in the Bahamas all wet refuse went overboard.  Only paper and plastic refuse went in the bin.  Contacting Geoff at Airhead, he said the Gnats in the compost bin was likely because of odor.  I probably need to use more COIR than I have been.  The toilet has gasket seals, but flies and gnats can get in when the urine bottle is being emptied or during use.  To kill the gnats Geoff recommended a thorough cleaning of the compost bin using boiling water.  I didn't have a way to boil a large quantity of water so I just used a strong bleach solution and let the bin soak for about 12 hours.  I re-filled the bin with more COIR than I've used in the past.  There are still a few gnats hanging around, but not like before.  The next time I empty the bin I'll use even more COIR (probably back to putting the whole brick in at once), but before that I'll go the boiling water route.

    Well the initial cleaning to remove the gnats did not work.  Within a week I had another colony in the composting bin.  Within two weeks a swarm was released into the head whenever I opened the trap door.  So I emptied the bin once more and this time did a much more thorough cleaning of the bin (using water and bleach) and the bottom of the toilet bowl/seat (using boiling water and bleach).  This time it appeared to do the trick.  After nearly 3 weeks no gnats come flying out of the bin when the trap door is opened.  As a precaution I spray fly/gnat killer into the compost bin every 3 or 4 days.  This is the kitchen version of the spray, so it is somewhat less toxic.  I've also gone back to putting the full brick of coir in the bin at the start of a cycle.  I add about 1 cup of coir every two or three uses.  That seems to have kept down the odor, which originally attracted the gnats to the compost.  This is definitely not a dump and forget toilet system.
    Even with these actions Gnats began to return to the compost bin within a month.  Now many, but one can become hundreds with a few weeks.  So I switched from the relatively mild kitchen insecticide to an outdoor fogger.  This shouldn't be used indoors, but I sprayed it directly into the bin, then closed the trap door and the sealed lid.  Not much, if any, of the insecticide was released from the bin.  After a few days of this treatment there were no more signs of the Gnats.  The use of the insecticide does not appear to have had any negative affect on the compost process.

    Well even the thorough cleaning and the use of insecticide has not prevented a Gnat recurrence.  It took longer this time (over a month), but I did finally get a swarm and once more emptied and cleaned the bin and the seat.  I am trying to figure out why I suddenly have this problem.  I can think of several possible causes, not one of which alone caused the problem.

    1. I'm in the real south now, and the south has a lot more bugs than further north
    2. Anchored out over the winter I was relatively far from shore and free of most bugs
    3. While anchored out, very little wet garbage made it into the garbage pail in the galley.  Most organic garbage was tossed overboard.
    4. I may have gotten a little lazy about washing the dinner dishes - leaving them in the sink for morning.
    5. Geoff Trott warned that flies might get into the compost bin while the urine bottle is being emptied.

    So in an attempt to control these pests I'm going to do the following:

    1, Use a separate bag for wet garbage and take it to the dumpster every day.
    2. Never leave dirty dishes in the sink for an extended period of time
    3. Use both of my urine bottles.  That is, when I remove the active bottle to empty it, I will immediately install the other bottle.  When I have emptied the active bottle I will clean it and make it ready to be installed when the other bottle needs to be emptied.
    4. Eventually move Sarah to a less buggy part of the world and go back to anchoring well away from the shore.

    After the third infestation I added one of those vaporizing bug killers (pic on right) to the compost bin before adding the COIR.  This item comes in a plastic cage and is meant to be hung in closets, alcoves and other closed places that are opened infrequently.  I removed the plastic cage and inside is a thin sponge which is impregnated with the bug killer.  After over a month the compost bin is nearly free of Gnats.  A few have gotten in there, but they don't seem to want to stay and they have not started a Gnat colony.  So while Sarah remains berthed in bug heaven I will continue to add one of these strips to the compost bin.
  • Final (I hope) thoughts on the bugs.  All of the approaches described above worked to one extent or another.  I've never had a bug infestation when cruising and anchored, only when dockside for an extended period of time.  Sterilizing the bin and seat with boiling water does kill the bugs, but they can still get back in over time.  Sterilizing is inconvenient if the bin was recently emptied.  So now I just keep a number of the bug foggers on board.  If I see a bug in the head, I set off the fogger the next time I leave the boat for a few hours.  I set the fogger near the air intake on the toilet.  This sucks the spray into the bin, but there is also plenty of spray in the head for the bugs that flee the bin.  Two days later I set off another fogger, to kill the bugs missed the first time and any that hatched since.  I repeat that one more time.  Normally that gets rid of them for an extended period of time, but as long as remain dockside they will be back.
  • Don't try to stretch the time between compost bin emptying.  As the bin gets full the composting process seems to be less effective.  That's when the odors can start.  For now I will empty the bin every 6 weeks even if it does not appear to be very full.  COIR is cheap.
Full-Sized Toilet Seat
At the 2009 Annapolis Boat Show I got a chance to see the full-size toilet seat now available for the Airhead.  This had been my only real complaint about the Airhead, so I immediately negotiated a swap-out of the compact seat on my toilet for the full-sized one.

Full-Size Toilet Seat
The picture on the left shows the new seat (actually a new upper unit) installed in Sarah's head.  As you can see it really isn't much larger than the compact seat (pics above).
I retained the original compost bin and the Urine bottles.
The seat on the new upper unit is actually a standard toilet set as you can purchase at Lowes or Home Depot.
Full-Size Toilet Seat

Gasket Seal on Full-Size Toilet Seat Lid
However it has been modified for use on the Airhead by the addition of gaskets under the lid and the seat.
So if this seat should break I could buy a replacement at most home improvement stores, but I would have to make some modifications.  It might be easier to just order a replacement from Airhead.
Fixing an Installation Error
If you go back to the installation of the vent you will see the most significant error I made in the installation.  I had to fit a piece of cleat stock to provide a flat surface to attach the vent fan housing.  In the process of trying to fit the cleat stock to the cabin roof stiffener the cleat broke.  Instead of making a new piece and trying again, I elected to install the cleat as is.  This left a significant air gap between the cleat and the stiffener.  I didn't think that was signicant at the time and I didn't notice any detrimental affects for several months.
Then in the fall of 2008 Steve Angst and I moved Sarah down the ICW to Melbourne, FL.  I don't know if it was the fact the head was being used by two people instead of one or it was just having another nose on board, but we both occaisionally noticed that there was a definite order in the cabin from the head.  I couldn't figure it out.  When the odor was noticable in the cabin I could not smell any odors in the head.  Clearly the odor must be coming from the deck vent.  At first I thought the air coming out of the deck vent must be flowing back into the cabin through the forward companionway.  This fit the symptoms, as the odor was most noticeable around that companionway.  Still, that didn't make a lot of sense as the vent was down wind of the companionway and the odor occurred even when the forward hatch was closed.
I was stumped on why the odor was happening, and then by the time we got to Charleston, SC the odor was gone.  I spent most of that winter at anchor in the Bahamas.  During that time I never noticed any odor in the main cabin that might have come from the head.
In 2009 I berthed Sarah in New Bern, NC and spent the following winter there.  Over the winter, with all hatches closed because of the cold temperatures, I once again noticed odor in the cabin from the head.  Again I couldn't figure out where the odor was coming from.  Although this odor was annoying, it really was no worse than the odors coming from most conventional marine heads and holding tanks. 
Then during one storm I noticed water leaking around the forward companionway.  I removed the trim around the hatch opening to find the source of the leak, and discovered the source of the odor.

Air Gap in Bulkhead
There is a small insert in the bulkhead aft of the head.  This insert covers the notch in the head comparment that I used for the vent.  It was replaced as part of the bulkhead replacement in 2004.  The replacement insert does not extend all the way to the underside of the cabin roof and does not seal that notch from the main cabin.  You can see the air gap between this bulkhead insert and the cabin roof in the picture on the left.
With the air gap in the cleat stock to which the vent housing is attached and this air gap in the bulkhead it was clear where the odor was coming from.  The best solution to this problem was to remove both air gaps.  Filling the vent housing air gap would be difficult, so I elected to attack the bulkhead air gap first. 
I used a can of window and door insulation foam to fill the gap.  This stuff cures to a soft piable state.  Other foam cures to a hard sandable surface.  I didn't want to add a sanding and grinding step to this project and went with the soft-cured foam.  I was able to remove the excess foam with a putty knife. 
The picture on the right shows foam during the curing stage.
This fix did eliminate head odors in the main cabin.  I still have not addressed the air gap under the vent.

Bulkhead Air Gap Filled with Foam
Filling the Air Gap

Vent Air Gap Filled with Rope Caulk
With the gap between the bulkhead and the deck filled with foam the odors were now drifting into the head.  This attracted a lot of flies and gnats into the head. 
I thought fixing the air gap under the vent would be difficult, involving a lot of fitting of small pieces of wood.  Then I remembered the rope caulk I used to the stay sail tracks on the coach roof. 
I pushed a lot of that stuff into the gaps and then re-mounted the fan and vent hose. 

This has finally removed the odors from the head.
Broken Agitator
In January, 2013 shortly after I arrived back in Jacksonville for the winter, I discovered that the agitator in the compost bin was not turning although the handle was turning freely.  Obviously something was broken.
I sent an email to Geoff Trott describing the problem and he replied that they had a few problems with the original agitator and had re-desgned the handle connection.  He then sent me a replacement agitator.

In the picture on the right I have removed the old agitator.  In the center of the picture is the crank handle and small socket.  The socket has been drilled down the center and screw was used to secure the socket to the end of the agigator.  The handle is inserted into the socket to turn the agitator.  This worked fine for nearly 4 years, but then it appears the threads in the agitator were stripped disconnecting the handle.  Having removed the agitator I believe this problem can be repaired, but since I have a new agitator I proceeded to install it.

Agitator Removed From Head

New Agitator Installed
In the photo on the left I have installed the new agitator.  The installation required expanding the hole at the handle end from 1/2" to 5/8" to accommodate a larger bushing.  That was easily done with a step drill bit.
The picture on the right is a closeup of the crank handle on the new agitator.  The handle is secured with a hitch pin rather than a screw.  This should not have the problem of stripped threads as did the old agitator.
Crank Handle Attached with a Hitch Pin
Diatomaceous Earth
In spite of the actions described above, at least once each year since I moved Sarah south to North Carolina, The Bahamas, and Florida I get a bug infestation in the compost bin.
When this happens I use a bug spray to keep the little suckers at bay until I can empty the compost and then sterilize the bin, seat and the vent hose.  This is not a big deal, taking less than an hour to accomplish, but I have been looking for something that would completely eliminate the problem.
In July, 2014 I got an email from some other cruisers who also have an Airhead.  They recommended using Diatomaceous Earth to kill any bugs that get into the compost bin.
I had never heard of this stuff, but with a quick search on the Internet I discovered that it is not only an insect killer, but is used as a water filter in swimming pools.  Both Home Depot and Lowe's carry the stuff, but in 20 LB bags for the pools.  The Internet garden supply store I used to purchase COIR also carries this stuff in a more convenient 4 LB size, which is shown on the right.

4 LBs of Diatomaceous Earth
I have just started to use the stuff since I saw a few gnats in the bin.  I wasn't sure about how much to use, so I added about 2 cups to the bin.  Immediately the gnats started to exit the bin, so it's apparent they don't like it.
I guess I'll know in a week or so if it is truly effective.  If there is one gnat today, there will be hundreds in a few days.
In the year since I added this stuff to the compost bin, the infestations have become reduced, but not eliminated.  It appears the effectiveness of Diatomaceous Earth as a bug killer diminshes as the compost bin is filled.
After 9 Years
2017 will complete the 9th year I have been living onboard with the Airhead.  I've learned alot, have had a few issues but I still would not consider replacing the composting toilet with a holding tank.