The Desiccating Head

rev. 7-24-2024, 10-5-2025

Three years later I'm still thrilled with this for a daysailor and even for weekend cruising on a small boat. Basically, anytime the alternative is a port-a-john.  

• Less odor. Practically none if properly managed.
• Lighter by 2-3 times.
• Easier to service. No lugging the whole thing off the boat. Just bag it and toss.
• No winterizing.

 I built mine largely from fiberglass, because I had the tanks handy for free, but plywood could be very good if well caulked and then well-painted. It really does not get messy in there.

 

 My Stiletto 27 had a portable toilet that stunk. Use the right chemical and it stinks less. Every time it is used a laborious haul/dump/clean process is triggered.

My PDQ 32/34 had a nice holding tank system that I had engineered to perfection. No odor, nearly like home. But it required space and weighed a good bit. Perfect for the PDQ, but totally unsuitable for the F-24.

We really only day sail the F-24 trimaran, and the head is only for emergencies. It didn't get used for years at a time, so we switched to WAG bags. Never used them.

 I'd been poo-hooing composting toilets for years. I'd experienced some nasty ones in cabins and some friends had a bad experience with a Natures Head. In fact, both failures probably included elements of design and operator error.

I was asked to investigate the topic, and so I did. There was a long-winded article in Practical Sailor last month, covering both toilet design, absorbents, and anti-odor additives for the urine tank.

 There are two keys to function:

• Separate the urine from the solids. First, the smell is greatly reduced, and second, the solids side it much drier, preventing it from getting wet and aerobic.
• Dry the solids. Like any animal dropping, once it is dry on the outside, there is little odor. That is the function of the absorbent; to speed drying, filter the air, and cover. It is NOT to cause composting. This is a desiccating toilet. 

There simply is not room on a boat for true composting toilet. The process tanks months, requires temperature and moisture control, and continuous mixing and ventilation.  Since you cannot effectively compost, then stop pretending and dry the waste instead. You can then take it home and compost it if you like, or double bag it and dispose of it like litter box scoopings. Your choice. The urine is odor-free once treated (see below) and can be disposed of easily.

I built a test version from a storage tub, a bucket and scraps to test the absorbents and additives. It was a crude thing, but in fact I used it in the basement bathroom for two months, during which it proved to be amazingly odor-free and easily to deal with. I was stunned. It was time to eat a large helping of crow. But I was happy to eat the crow, because the result was a truly user friendly head solution for my F-24.

 

  

A perfect fit. Note the shedded aspen pet bedding, TP, and spray bottle of citric acid to the right. Necessary supplies. 

  

 

The final version was based on molded parts from Separatte, a fiberglass tank I modified to fit the available space, an under seat baffle I cut from fiberglass, and yes, a bucket and jug. The top hinges up for service, which is a simple matter of lifting out a bag and replacing it; a clean, contact-free process. The absorbent of choice, at any price (I tested many), is millwork sawdust and shavings I get for free (aspen bet bedding is also very good). The urine treatment is citric acid, though vinegar and Nilodor are also very good.

I no longer see any point in conventional portable toilets, at all. A desiccating toilet is better in every way. Regrettably, you must either pay a king's ransom or build your own.

 

The separator kit from Amazon.

 

The general arrangement. The body of the head is a modified fiberglass battery box, so it is watertight and easy to clean (hose it out). The hinged lid is heavy plywood, well painted. The bucket was cut down to fit. The urine jug was something I hunted for a perfect fit. I added a butyl rubber grommet made from a truck inner tube.

 

Proper operation includes covering the solids with a thin layer of wood shavings (aspen worked best, after testing many materials in a prototype). The primary function of the cover is to wick moisture away from the surface.

 

Odor can be even further reduced, to zero, by hanging a small mesh (I used tramp fabric) sachet of swimming pool bleach inside the box. Moisture triggers a very, very slow release of chlorine, which oxidizes any odor. It lasts about a year. (Black bag on the back left side, hanging from a hook.)

 

I tested it in a spare bathroom in my house for a month before taking it to the boat. Honest, no odor if operated correctly. The spray bottle is ~ 1% citric acid to lightly rinse the urine separator; kills the smell and prevents the scale build-up common in urinals. 

 

These are the internals of the C-Head, now out of business (owner passed away). 

 

 

In praise of WAG Bags

On my last boat I had a conventional holding tanks system, and properly maintained and designed, I believe it is the best answer for most cruisers. I've done lots of research, used composting heads, and have no reservations about this recomendation. But with my new boat, the right answer is WAG bags.

WAG (Waste Alleviation and Gel) bags are widely used by the military and FEMA in situations where conventional sanitation practices aren't practical. For example, I used antifreeze in the toilet of my PDQ in the winter, and that worked well, but carrying a portable toilet on an icy dock from my F-24 seemed pointlessly dangerous. So I investigated WAG bags as a winter alternative.

A heavy duty bag and a gel very similar to that used in diapers. Pretty simple. We have a portable toilet, but we don't put solution in it anymore. These are simpler.

Not pleasant, to our western sensibilities. But think of the plus sides:

• Light.
• No head to clean.
• No odor once off the boat. 
• No pump-out station, no lugging the portable head home to clean and refill.

I'm not saying they are for everyone. We hardly ever use the head on the boat. We hit the shore side toilets before heading out, and if we drink some beer, that goes over the side. I doubt we use more than one bag a year.

But even when cruising, I would have kept a box onboard for emergencies, had I known of them. They can be laid right in the head (drain and clean first, obviously) or used over a bucket, no mess.

Not pretty, but darn functional.

Something Lazy, Something Free

Free is always good, except this is not quite free.

Or rather, it is free if you use any sort of holding tank treatment chemical.

 I've done all sorts of holding tank stuff for Practical Sailor Mag. Chemicals, hoses, vent filters. Fun stuff. And in the process, in addition to learning all sorts subtleties, I solved all of my own odor problems, save one; odor from the bowl itself. If I flush with seawater and leave it a few days, there's some stink; sulfate in seawater is converted to hydrogen sulfide by millions of wee bacteria. If I flush with fresh water, it's better, but not zero; I guess something sneaks back down the waste hose, or perhaps up the feed hose. And either way, the bowl tends to get ratty, as marine flush volumes are limited and the water isn't chlorinated. I hate scrubbing.


Place a 20% solution of holding tank treatment in a spray bottle and mist the bowl down with each use, or at least each day, or and certainly whenever you'll be leaving the boat for a while. This cleans the bowl, treats the water in the bowl, and treats the water in the waste hose, preventing stink. And since it's the same treatment you would be using anyway, just subtract this from the usual dosage.

 I haven't scrubbed in months; the treatment eats the waste off. Very lazy.

 
However, not all treatments work.

Pick an scent you like, preferably very mild. I like Forespar Refresh and Raritan CP, but Camco TST Ultra-concentrate is our favorite. These are compatible with any type of holding tank treatment, including bacterial treatments. I tested a bunch for Practical Sailor Mag (February 2012 and December 2012).

• No blue sterilizing treatments, containing with formaldehyde and the like. Toxic, smelly, stain-prone, and well... gross. Too much like a portable toilet. Very tough on joker valves. Formaldahyde is listed as a human carcinogen. I don't understand why they still make these. Ban them from your boat.
• No bacterial treatments, like Bactank T3 or Happy Camper. They grow in the bottle and get gross. They are quite effective in the tank, just not for this.

Less work. Less money.

"A Bathroom Fan": or "No Blog Could be Complete Without a Tale of Head Repairs"

Well, as much as I enjoy fiddling with engineering solutions for my sailboat, I could go a lifetime without providing basic services and solutions in the head area. It simply didn't work out that way.

When I bought the boat the head worked fine. Actually, it was well below freezing during the pre-purchase survey and all of the water systems were winterized. However, we used the head throughout the winter and spring and never had any difficulty with it. Tip: flush with a very weak solution of antifreeze and you won't have to worry about freezing anything. Gradually - I tried very hard to ignore this gradual development - we started to notice a wee little bit of back-flow. Eventually it became whole lot of back-flow. No matter how you flushed, eventually something that no guests wish to speak of would find its way back into the bowl. Each user, of course, assumed that a prior user had either been hasty or just lazy about reading or practicing instructions. In reality, the joker valve had worn a bit, allowing some back-flow from a holding tank. I have no idea from whence the term "joker valve" derived. It is what engineers refer to as a duckbill valve, a piece of rubber so designed that wastes can flow from the inside out, but then closes tight against the back flow. Because they can seal around debris, they are commonly used in wastewater lines and storm water lines, particularly those that discharged into tidal waters - they prevent a rising or flood tide from backing up the sewer. I digress.

One nice thing about the PDQ is that the head compartment is also a molded shower stall, and so everything - I won't go into details - is easily hosed down the drain. Replacing the valve is a five-minute 2-screw task; just not the most pleasant five minutes you've ever spent. But that was the problem and the major source of stink was thus terminated. By the way, my friends an I have durability tested all of the major brands (it turns out that many are 100% interchangable in Jabsco Manual Heads) over the past 5 years and determined that the Raritan PH-II valves outlast all others by 3:1. You should get 2-4 years instead of 1-2. $21.50.

Still, a head will never be fresh as a flower. Space on the boat is necessarily tight - at least with my budget - and a little positive ventilation would be a good thing. The boat does have a number of solar powered ventilators; unfortunately they all pull the air from the bathroom through the cabin, and out through the aft cabins. A bathroom fan seemed like a good idea, but I did not wish to cut another hole in the deck.

The solution was simple; the compartment behind the toilet contains only the holding tank and a hot water heater, and it already has a solar powered ventilator. All I needed to do was provide a small fan and louvered opening that would convey the bathroom stink into this compartment where it would do no harm and would be exhausted. Yes, I have all sanitary rated fittings and hose, but for a small compartment dominated by a holding tank you must have realistic expectations. It isn't bad at all, but I would serve tea there either. I once read of a sailor that had a spare berth in that compartment - for the himself, the captain, he explained. Oh, my.

The vent louver is from Sea Dog, a 3-inch diameter, flush-mount, ABS round vent available for $2.99 from Defender Marine. The fan is from Radio Shack, $17, a 3-inch diameter 12 V computer fan. By some incredibly lucky quirk of fate, the 4 mounting bolts for the louver and the fan are exactly the same, both in diameter and spacing. Is a computer fan suitable for a damp environment? I have used these Radio Shack fans to draft compost bio-filters on animal enclosures, a similar duty, and they typically live through about 4 years of continuous duty. That is right up there with "marine" products. Using a 3 1/4-inch hole saw to pop a hole in the bulkhead and four #8 x 2-inch flat head machine screws, both the louver and a fan were mounted in minutes. Well, not quite that simple; the box for the louver will tell you you need a slightly smaller diameter hole saw, which is not true, and in fact even with the 3 1/4-inch saw I had to work it at some odd angles to make the just a little bit larger than 3 1/4 inches, perhaps 3 3/8 inches. Not a big deal, just measure carefully.

The head bulkhead is FRP with a balsa core, so it is a good idea remove a little core and seal the edges with epoxy, just in case. This is far above the waterline and on the interior, but it is a shower compartment, so it's better play it safe.

Should you desire to duct the fan through a hose, the same louver is available with a hose barb. You could simply cut out the louvers, add it to the discharge side of the fan using 1/4-inch longer screws and be in business.

While I was pulling wire, I elected to add a small light in the holding tank compartment. Fishing poles are stored in there, and it is also home to all of the through-hull fittings; a light is useful. I picked up a cheap pick-up truck bed work light with an integral switch from Advance Auto Parts (~ $7) - not marine perhaps, but I had used the same light on a previous boat as an under-boom light and it held up very well. Since this is a very dry location I am not concerned. Others have used automotive back-up lights in damp locations with success; I am not certain how they would be on deck with salt spray, but inside lockers with a little grease on the terminals they should do very well.

A few notes on marine wiring, for the uninitiated:
* Turn all of the power off and make sure to check that this is true with a multi-meter. It may only be 12 volts but there's a lot of amps available, particularly when you are tapping into the main panel.
* Use the same multimeter to be certain you know where the ground is and where the hot side is. Don't be casual about fusing; it even easier to get overheated circuit 12 volt applications as it is in a household. Make sure you are not on the 120 volt side.

• Mark the hot wire at the panel end and match the existing color code.
• Use only crimp connections or screws/nuts attach toe terminal strips. No wire nuts. No wrapping two wires together and covering them with tape. No solder-only connections. If you feel like soldering over a crimp connection, it will do no harm, but solder-only connections can come apart when overheated. Crimp connections formed with the good ratcheting double crimp tool effectively form of cold weld and they been proven to be more reliable than any other practical connection. Do not use pliers to form a crimp; it is not as good, no matter what you have been told. The wire should not pull out of the crimp without breaking.
• Use ring fittings if possible. They are safer. If you cannot imagine getting the terminal screw out, use a spade fitting, but only a flanged spade, with the ends turned up. Straight spades come out too easily and are not approved by the code.
• Use only tinned marine wire, automotive primary wire, or machine wire ( the multi-stranded sort used in conduit). Solid household-type wire will eventually snap from repeated bending. Extension cord wiring has completely inadequate insulation. Only the first two wire types are approved for vibrating applications (motors and engines) and tinned wire is suggested in all damp applications; the tin serves as galvanizing for the copper and prevents the copper from turning black and developing high resistance connections. Although machine (THNN) wire as sold at Home Depot on spools is not suitable for use directly on motors, it is approved by both the Coast Guard and the National Electrical Code for use in boats. A short pigtail of finely stranded wire is used to connect the motor (which comes with the motor, in this case).
• Use waterproof grease on all connections in damp areas. It sounds like it will block current flow; it will not in clamped joints. It will block water, air, and hence electrolysis, which is the big enemy. Vaseline, bearing grease will work.

If all of the above is not obvious, read a book on 12 volt marine electrical wiring. It's straightforward, but deserves study. Marine practice and automotive practice are a little bit different. I've left much out.