The Online Magazine For Amateur Boat Builders














Marine Toilets
by Rob Rohde-Szudy

Few online forums delve into the tricky bits of this "unmentionable"
subject. We should. It is necessary in many cases, and always seen as a necessary evil. I hope to eliminate the evil associated with the marine head.

Ocean cruisers have big problems here. They don't have space for storage tanks or anything like that. They are pretty much limited to pumping barely treated waste directly overboard. I believe this is a tremendously bad idea, but passage-makers might be stuck.

We inland lake folks have things a lot better. We can use RV tank technology and pull our trailer up to the dump site at campgrounds.
Theoretically this is easy, and many people are accustomed to the procedure. I personally hate this option and find it disgusting. We inlanders can also use porta-potti type chemical toilets. Again, I find this woefully inadequate, as it rather impairs one's enjoyment of the fresh air.


I think there's a much better way to do this, at least for us inland lake folks. Possibly for ocean cruisers too, if they can work it out.
Best of all, it's so cheap that nobody is bothering trying to sell it to you.

The fundamental flaw with all these systems is that they use water.
When you add water to human waste, you invite anaerobic decomposition.
This produces methane and hydrogen sulfide. Those gasses are the nasty "septic tank" smell we all hate. You can try to cover the odor, but it will always be there where there's anaerobic decomposition.

AEROBIC decomposition is a whole different animal. Literally! It's a different family of bacteria. These do not produce the odoriferous gasses. This process is best known as composting.

"Oh yeah," you say, "I've seen those $1,000 composting toilets. No thanks." I agree. But think about this - composting is a simple process that thousands of gardeners do routinely with no more than a few buckets and a heap of stuff enclosed by some cast-off shipping pallets.

Here's a solution that's up our cheapskate alley.


  • 3 or more 5 gallon buckets with lids
  • A toilet seat
  • Damp sawdust or wood shavings (No toxic chemical included! Just wood!) A place for a compost bin
  • 7 or more scrap pallets
  • Wire to tie pallets together (The last three can be replaced by knowing someone who's really into

Here's the whole system:

Building it is a 30 minute job. You cut off the top rim of one of the buckets, so it will slip inside the other in-tact buckets. Cut some chunks of 1x2 and notch them to hold that rim to the bottom of the toilet seat. Nothing to it.

Right now you're starting to think I've finally gone off the deep end.
But bear with me a bit longer…

In use, it is simplicity itself. Start with a couple inches of sawdust in the bucket. Make your "deposit", cover it with sawdust. The damp sawdust acts as a biofilter, and there is no objectionable smell! It mostly smells like pine - a smell with nice associations for folks who make a pastime of cutting up wood and making it into floating boxes!

I was amazed too. It seems like it would smell, but remember that it's the anaerobes that makes it smell. If you smell that sewage smell, your bucket is far too wet. Add sawdust!

I gave this thing about the most difficult test you could imagine. I used it for my whole family in a small apartment with virtually no air circulation. I figured that even if it smelled a LITTLE there, it would be fine under better circumstances. To be honest, I found it less objectionable than the water toilet. Neither smelled, but I swear that the flush toilet is designed (by someone with a sick sense of humor) to be an amplifier. And of course, with sawdust there's no flushing sound to announce to the world that you're done. I never realized how much those two attributes of the flush toilet annoyed me.

Now that you've read my glowing review, let's go into the details for the 10% of you who are still reading. You people must be cheapskates indeed! (Here's to you!)


When the bucket is full, move the seat to the sawdust bucket you just emptied, close the full bucket, and open a fresh bucket of sawdust. You don't need to underfill the sawdust buckets, as the waste seems to fill the spaces between the sawdust, adding little or no volume. In fact, you probably won't even have to switch buckets for a weekend on the lake. A family of 4 will most likely use about 1 bucket in a weekend.
Convenient, eh?

When you get back to the compost heap, make a little pit in the middle of the heap and dump the bucket in. Rinse the bucket with just a little water - less than a quart - and give it a quick cleaning with a toilet brush. Just a single spiral scrub. Dump the water in the middle of the pile. (Those bacteria get thirsty too!) This is also where you determine if you have been using the right amount of sawdust. What you dump out should be damp, but not wet - like a wrung out sponge. No, I don't suggest you check manually. But if it looks very wet, you could probably use more sawdust for absorption.

There is only one critical step: under no circumstances should the rinse water be flung aside nonchalantly! That's the one step where you might spread disease if you're not careful. If it goes on the pile, it will be OK. Also, never use bleach on the bucket, as it will kill the bacteria that make this all work. Soap is fine, and only when truly necessary. Use the biodegradable camp soap, and only a little. After dumping and rinsing, leave the bucket out in the sun for a week or so to let the UV light kill any remaining microbes. Then refill it with fresh sawdust.

The sawdust can be stored outdoors uncovered perfectly well. It actually works better if it's starting to compost on its own.


Well, no. Marine regulations are about what you can discharge overboard. Nothing in this system is discharges overboard. You can even use it in your house, because the law governs "waste disposal", and what we're doing here is "resource recycling". In fact, I DO use this in my house. It strikes my as incredibly stupid that we spend so much to get water clean enough to drink, then use it to carry our excreta through expensive pipes to a more expensive "treatment" plant, where their greatest problem is taking all that water back OUT, so they can treat the waste! And we wonder why our taxes are so high. I abstain from the madness and keep my resources at home where I can use them to fertilize roses.

Of course, you'll never talk a building inspector into the idea that this arrangement means you don't need a septic tank. On the other hand, a septic system should last just about forever when the solids were kept out of it entirely.


They are selling composting toilets. See www.sun-mar.com for one example. From what I've heard these units work great. But I'm not shelling out $1,000 for what I can do with $20 worth of buckets and toilet seat. It's COMPOST, not rocket science. People will try to tell that you can't compost human waste, but that's because they haven't tried it. In fact, it seems to me that the process benefits immensely from the added nitrogen.

I think the main reason nobody is selling this particular system is that there would be no profit at all unless you found some real suckers to pay far more than it was worth. The other reason is that it is not self-contained. You need to have a separate compost bin. But I think that this it exactly it's advantage on a boat, though. Less to carry around!


Joe Jenkins wrote the book on this technique. Literally! You can read it online at http://www.weblife.org/humanure/. The book is pretty funny in part, actually. Mr. Jenkins has been using this system at home for 25 years. He would even throw parties to "generate compost" when he was running low!

Says Jenkins: "The system of using an organic cover material in a small receptacle works well enough in preventing odors to allow the toilet to be indoors, year round. In fact, a full bucket with adequate and appropriate cover material, and no lid, can be set on the kitchen table without emitting unpleasant odors (take my word for it)." Take my word too. Like I said, I was amazed.

I did find I needed to use more sawdust than he recommends. His amount prevents odors perfectly well, but the contents of the bucket tended to get wet. Maybe I drink more than he does. Easily remedied in any case.


Basically, if your compost pile is steaming, it's making enough heat to kill pathogens. If it's not steaming, the pile is too dry or it's too cold out. Either add water to make it like a wrung-out sponge, or wait for warmer weather. It'll catch up in the spring. If it starts to stink, it's too wet. Leave the top off for it to evaporate. You probably don't need a top at all unless you live in the Pacific Northwest. Don't overdry it, though. It will take a little time at the right moisture level for the aerobes to catch up. Any other additives will probably screw it up. Kitchen wastes work fine. Meat too, even though we're told it can't be composted. Compost LOVES coffee grounds. Be careful of anything really acidic, though. If I had a whole lot of tomatoes, I'd try to spread them around in different parts of the pile to dilute the impact. You should have three bins. Much like the buckets, when one bin is full, start the next one. By the time the third is full, the first will be finished. If you find any unfinished pockets, put them in the bin that's getting loaded and run 'em through again. I don't think you need to turn compost. If you have to turn it, you didn't put in enough light material that can conduct air. Straw is ideal for this. Planer shavings are pretty good too. Weed stalks work surprisingly well. For a full discussion of this, click on the link to Jenkins' book above.


If you don't have a good source of sawdust, "pine bedding" for small animals is sold in plastic covered bales at pet food supply houses. It works fine. It's what I use. If you have a source of planer shavings or sawdust for free, so much the better. Just make sure they're not cutting any treated or painted wood. Some paints might be OK, but you don't want anything in there that might make those bacteria unhappy. If the sawdust has sat outside, so much the better. Sawdust works much better if it is at least partly rotted.

In fact, it needn't be sawdust at all. It could be peat moss, leaf mould, oat hulls, grass clippings, or any other loose organic fill that will prevent odors, absorb urine, and eliminate any fly nuisance. If what you're using doesn't work, try something else. I like the pine smell, so I pay a little for the pet bedding.


This system is great for us inshore cruisers, as we get to land to do the composting, and can easily carry a weekend's worth of buckets.
(Actually, this applies equally to and hunters, campers, fishermen, people traveling with potty-training-aged kids, etc.) We also don't have salt breeze to mask unpleasant anaerobic smells. Ocean cruisers might have more trouble with this method unless they budgeted a whole lot of space for sawdust and could compost onboard. Here the Sun-Mar system might make more sense, as it is self contained and speeds the system with forced aeration and heat. It would likely still be cheaper than a marine head, as the composting system costs very little in maintenance.
However, I suspect 140 degree rolls would present problems for any system.

This system might also present problems for apartment dwellers. You need a place to put up some compost bins. Or you need to know someone who does compost or can lend you space to compost. I do it on the currently vacant farm where I grew up. (Shh...don't tell anyone.) There are also high-end indoor kitchen composting systems available. I can't see how these would not work, but I'm not paying that kind of money for a glorified bucket with some holes in it. If your apartment has a balcony, one of those plastic bin composters could easily live out there. Again, I don't want to pay for a glorified bucket with some holes in it.

Unfortunately, you can't really compost in the buckets. In fact, you need to empty them into your bin as soon as practical. There's no air in the bucket with the lid on, so it will go anaerobic and stink! If I had to do balcony composting, I'd build a bin from a plastic 55 gallon drum, which I can get for $5 used from the local ice cream factory. You guessed it. I'd drill some holes in it! I might also plant a piece of the pierced PVC they sell for foundation drains in the middle to help keep it aerated.

For use on a boat, I recommend taking off the seat and keeping all buckets lidded when underway, in case of capsize. Find a good way to lash the buckets down as well!

Also, it would seem that color coded lids would be an excellent way to keep track of which buckets are used, and which are clean sawdust. I haven't really bothered with this yet, but I should. Lids are really cheap. I use the orange Home Depot buckets for the toilet buckets, so they cannot get confused with any of the other buckets I have, which are all white. I hope to find some black lids to alternate with the orange ones, so I can leave white for all non-toilet applications.

This may have seemed a bit off-topic, but I don't think it is. This technique can add much to the arsenal of folks seeking bargain-basement cruising comfort. Any questions can be directed to rob rohde-szudy at netzero dot net.