Dissecting the Desiccating Head

PS embarks on an excretionary voyage into the world of alternative, ‘composting’ toilet systems.

1

Our first cruising boat had a conventional portable toilet. We didn’t like it, but we made peace with it, cruising for up to two weeks at a time. Using the best treatment helped (see PS September 2018, “Controlling Porta-potty Odor).

Our next boat, a PDQ 32 cruising cat, had a holding tank system. We replaced the hoses with low permeation types (see PS April 2012, “Marine Sanitation Hose Test,”), and used the best treatments (see PS February 2012, “Solutions for a Stinky Holding Tank”). As long as we maintained the head properly, it was just like home. We were fortunate to have accessible pump-out stations in our marina and cruising ground.

Then, we downsized to an F-24 trimaran. Like our first boat, it came with a conventional portable toilet, and we didn’t like that. My back was 25 years older, so carrying it through the cabin and up to the dock was annoying, maybe even dangerous. Smaller toilets (a weight I can actually lift) fill up in two days, making them impractical for us. Weight isn’t the only issue with a portable toilet. You have to take it home, dump it, clean it, top off the flush tank, and bring it back to the boat. For the past three years we’ve used WAG bags deployed in the empty portable head. Because we were day sailing, they were only for emergencies, and we could always charge the portable with water and chemical and use that if we felt the need.

Composting toilets are growing very popular, and we’ve tested a few (see PS November 2002, “Composting Marine Heads”). They reduce odor by separating the urine from the solids and then begin a composting process. We concluded that they worked well, but on sailboats they technically function as dry toilets not composting toilets. A true composting toilet, as defined by NSF/ANSI standard 41, Non-Liquid Saturated Treatment Systems, provides actual composting and will reduce coliform bacteria to <200 MPN/100ml. This takes months of holding capacity, venting, controlled temperature, moisture, aeration, and mixing, and a lot more space and power than any boat can afford.

DRY TOILET TYPES

Dry toilets, more accurately referred to as desiccating toilets, take a different approach, eliminating odor by separating the urine from the solids, and then drying the solids to form a dry crust. As it turns out, most of the odor is generated when urine and solids are mixed, and by separating them, they can each be treated to avoid odor.

Properly treated urine has no smell —amazing, but true—and you can’t smell dried dog poop until you step in it (see page 18 “Additives Fight Urine Odor”). Separation is accomplished using a separating toilet seat that funnels urine away into a separate container and away from the solid waste (see page 16, “DIY Desiccating Head Options”). Composting systems use a mixer to chop up and blend the solids with the absorbent, making a mess you hope will start to compost. Desiccating toilets can take several approaches. The C-Head dry toilet uses a gentle wave motion to coat the solids with absorbent, the result is more like a cat litter box with lumps than a homogenous mixture (see page 23, “Clever C-head Downsizes the Waterless Toilet System”).

Non-churn systems allow you to line the container or bucket with a bag, making for truly simple servicing; no mixer to pull out or work around, no waste to pour into a bag, leaving no possibility of spills. This is a considerable advantage if guests or multiple users may make a mistake, inadvertently peeing in the solid waste side.

If urine and solid waste are mixed, you’ll need to start over to prevent odors, and this is easier if you use a bag liner. The down side of the bag approach is that you will need to add absorbent after each use. Additionally, if you leave the boat for more than a day or a few, it is best to empty the bin, a bag makes that easy.

All of these dry “treatment” options that involve separating liquid and solid waste will allow you to cruise longer than you could with a conventional portable toilet. Even the smallest waterless toilet system can hold a week or two. The larger ones can go weeks without requiring a shore stop.

This convenience doesn’t come cheap. You’d think the few pieces of plastic required to assemble a desiccating toilet would cost less than a quality portable or inexpensive marine head, but in fact they are 5-10 times that price.

Fortunately, there are DIY kits that include key parts, like a molded plastic urine diverter, so your DIY project will have a finished appearance. Our F-24 had a tiny space allotted for the head, commercial units were too expensive and not the right shape, and having designed municipal waste treatment systems, including odor control, I thought would give it a go, from optimizing the treatment chemistry to building a supercompact DIY unit.

Disposing of Desiccated Waste

Composting is a misnomer for dry toilets used on boats. They are desiccating systems, like a litter box, and the waste is only dried. Every few days to few weeks, and anytime you leave the boat for more than a day or two, you should empty the bin.

For day and weekend use, we opted for the no-churn method and bagging the waste. Initially we used WAG bags (see PS September 2018). These are a double bag system, with a 1-mil inner bag and a 2-mil outer Ziplock bag, plus an absorbent to contain liquids. (We bought them without absorbent and used our own).

Because the urine and solid waste go in the same bag during standard WAG bag usage, and they are gelled but not dried, a sturdy bag system is required. However, using the PS dry toilet design, the bucket waste is very dry and didn’t even stick to the bag, so we switched to quality kitchen bags and double bagged for disposal, just to be safe.

Common sense says don’t use the small waste bin by the marina office or the garbage can near the dinghy landing for your toilet waste. Walk it to the main dumpster.

If you still feel guilty, consider that the EPA estimates that 1.5 percent of the domestic trash stream is disposable diapers. We are not aware of any specific federal regulation regarding small quantity waste disposal from desiccating or composting toilets.

You can, of course, transport your bagged waste home for flushing (in small ‘doses’ only), using for compost, or adding to the trash bins. Alternatively, you can skip the bags, get a second bucket with a lid, and consider the churn method (see C-head review, page 20). True composting is more complex, and will take 6 months on the average. Do not use the finished compost for food crops, because human pathogens are still possible. Control access and run off.

As for the urine, taking the jugs ashore is simple. Some marinas forbid the disposal of portable toilet waste, but they’re taking about the blue-treated mess from a conventional portable toilet. Yes, many users dump it over the side. However, this is forbidden inside the 3-mile limit and there really is a lot of nitrogen and phosphorous in there. At the very least, avoid poorly flushed harbors.

OBSERVATIONS

Physiology differs and some will find it more difficult to get everything in the right spot. Sometimes it helps to urinate first, somewhat forward on the seat, and then slide back as it becomes mission critical.

Start with about two cups of absorbent in the bag. Cover the solids with about one cup of absorbent first, before adding TP, and then another cup of absorbent after. There’s no harm in using more absorbent, it will just fill the bucket sooner, but you will soon learn that you need less than you think.

Alternatively, you can place the toilet paper in a separate resealable bag to save space in the head. Doing this will reduce the amount of absorbent needed and the desiccation will dramatically reduce the waste volume. We found that a 3-gallon bucket will last one person about 10 days, toilet paper and all, assuming the toilet is used exclusively. A 5-gallon bucket should easily last two people one week. If you dispose the toilet paper separately, it will last 2-3 times longer and smell slightly less because the absorbent is more effective at controlling odor. We tested both ways, and concluded it comes down to personal preference and needs.

Spray the urine diverter with treatment after each use. A spray bottle filled with 5:1 – 10:1 dilution of one of the odor treatments recommended in “Additives to Fight Urine Odor” (see page 18). The chute in the back does not get soiled and does not require cleaning. It is only there to prevent a mess in the event of a stomach bug.

Solid waste should not be left in the toilet if the toilet is not going to be used for more than a few days. Empty the toilet every week regardless of how full it is and leave it clean if you are going to be away. Really, there is little advantage to being able to store large amounts of waste in the toilet. It only means a more difficult process when emptying becomes inevitable. Compost the waste outside in a compost tower or discard it (see below, “Disposing of Desiccated Waste”). If it is wet it will stink; this is rule number one. The drier you keep it, the easier it will be to empty the bucket and keep it clean.

Venting can help, but generally is not needed if the container is sufficiently dry. Following that thread, we experimented with keeping a container of calcium chloride or silica gel adsorbent cylinders (see “High and Dry for the Winter,” November 2012) in the enclosure (but not in the bucket itself). Yes, it seemed to help, since the drier the absorbent and the deposits, the less potential for smell. But do not add desiccant (silica gel or calcium chloride) to the bucket itself; we are trying to pull water out of the bucket, not draw it in. This is why we want a cover material with good wicking characteristics.

CONCLUSIONS

Using any of the recommended urine treatments and bowl sprays, we experienced zero odor for at least 3 days, and greatly reduced odor for up to a week. There is no reason to leave the jug longer than that. Mill work shavings are our favorite solids media, but many things will work, according to availability and personal preferences. Placing TP in a separate bag reduces odor by improving coverage and reduces volume by several times, but it works either way. We let short-term guests do as they like; if they can separate the pee and the poop, that’s victory enough. Hanging a small pouch of a pool chlorine powder inside the rim also reduced odor.

We had low expectations when we started this little project, procrastinating for years. How could a bucket ever serve our needs, in other than the crudest sense? In fact, we were stunned by how efficient desiccating toilets are. It suits our daysailing and short-term cruising needs far better than any portable head ever did. Odor is nearly zero, use is simple, and clean-up back at the dock simpler and less unpleasant; just seal the a bag and pitch it in a dumpster, and dump the urine in any toilet. We can see no advantage to conventional portable toilets, other than economy. Hopefully, with increased demand prices will fall, since they are simple constructions.

Desiccating toilets may also be superior to holding tank systems for sustained cruising in areas, such as freshwater lakes and estuaries, where pumpout facilities are far between. Some advocates prefer desiccating toilets for all applications, but we still see merit in a well designed holding tank system for larger boats cruising longer distances.

Clever C-Head Downsizes the Waterless Toilet System

Composting takes time and space. We tested Air Head and Ecolet (“Composting Marine Heads,” November 2002) and found them functional, efficient, and a good bit bigger than traditional marine heads. And although the composting process certainly gets a start, it won’t get far in a head that is in continuous use.

A first glance, the C-head looks like a gussied up seat-and-bucket, but in fact they paid great attention to design basics. Instead of a horizontal mixer that tears through the waste, breaking it up, the motion gently rolls the waste into the media, covering it and eliminating odor without making a mess. This makes the bucket easier to dump and to clean.

For daysailors, bags are less messy to use, but you can make a bag-ready conversion for daysailing by simply putting a 3.5 gallon in place of the 5-gallon bucket or by cutting out a half moon section of the rim of any 5-gallon bucket to accommodate the urine funnel.

Visit the C-Head web site for information and a full discussion of the relative merits of churn and churnless methods (www.c-head.com/post/churning-vs-churnless-versions).

As we have explained, the same process can be accomplished without churning, but it uses more media and the user will have to cover their waste after each use.

C-head sells far more churn than churnless models, but they do make churnless models ($35 deduction).

Bottom line: We found the C-head to be well-finished and sturdy, and we couldn’t think of anything about it we could improve. Simple is good. Price is $699 for the basic churn model.

Darrell Nicholson is Director of Belvoir Media Group's marine division and the editor of Practical Sailor. A lifelong thalassophile, he grew up sailing everything from El Toro dinghies to classic Morgans on Miami's Biscayne Bay. In the early 90s, he left a newspaper job to sail an old gaff-rigged ketch across the Pacific and has been writing about boats and the sea ever since. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida.

1 COMMENT

  1. Hi Darrell, thanks for the article. Could you offer a link or hint where I could follow up on “… there are DIY kits that include key parts, like a molded plastic urine diverter…?”

    I am contemplating longer (> 2 nights) stays on my 1995 Hunter h23.5, which was originally equipped with a 2.5 gal. Dometic, similar to your Corsair.

    Seems like maybe there was some info in the print magazine and that didn’t make it into this electronic version. ?

    BR, Tom

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