Marine Composting Toilets

Marine composting toilets offer one possible solution for dealing with the difficult problem of human waste aboard a boat.side view gray background

There are several makes and models, but the principle is the same. Solid waste, including toilet paper, drops down into a lower chamber beneath the toilet bowl. A trap door keeps the contents hidden between uses. In the lower chamber, waste is mixed with a composting medium, such as coconut fiber. The user turns a handle on the side of the toilet, to mix everything together after each use. This speeds up the composting process.

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urine flows forward, down the drain holes shown. Solids fall down through the trap door (shown closed here).

The key to the success of marine composting toilets is the separation of urine and solids.

When placed together in one tank, urine and feces produce an intensely bad odour. Anyone who has used a porta-john or outhouse knows this only too well. When the urine is diverted away from the feces, odour is reduced dramatically. To be blunt, wet poop stinks and dry poop does not. By separating urine from feces, most of the odour problems surrounding boating sewage are eliminated.

Urine is typically diverted to a 2 gallon bottle, which is, in effect, a small holding tank. This bottle will have about 2-4 days capacity for two people. Some boaters carry an extra urine bottle to extend this capacity.

Urine does not pose a health risk, and can be easily disposed of ashore in any toilet or pump out station. As a last resort, urine can be discharged legally, the proper distance from land. While there is no significant bacteria in urine, it does contain concentrated nitrogen – which can cause algae blooms in stagnant water, so it should never be dumped in a bay or any anchorage under any circumstances.

The fan is the critical component in any marine composting toilet installation.

There is usually a small 12 volt fan built in to the toilet. This pulls air into the toilet from the bathroom area, and exhausts it outside through a vent. The purpose of this is two-fold. First, air moving through the composting chamber removes excess moisture. The solid material shrinks dramatically as it dries out (just like a pile of grass in your backyard composter). Because of this shrinkage, the toilet can hold a surprising amount – estimated as 60-80 solid uses. Two people living on their boat full time would need to empty the toilet only about once a month or so. If the boat is only used for weekends and holidays, you might easily go the entire summer without emptying it at all.

Secondly, the fan eliminates odour. Air is being pulled in to the toilet from the boat, rather than wafting up into the boat. Even with the trap door open, air (and smell) is not escaping into the boat. It is going outside. peat moss in toilet compartment smaller file

Boaters are understandably concerned about power consumption. A marine composting toilet uses a small computer fan that draws about 2 watts. If this amount of electricity usage is a problem, you can install a solar vent. This is a small vent with a solar panel and battery built in. It works even on cloudy days to charge the battery, and the fan will go 24/7 without draining your main batteries. Another solution would be to install a small solar panel to make up for the electricity used by the toilet.

When it comes time to finally empty the toilet, you undo two clasps and remove the upper section. Place a compostable ‘plastic’ bag over the top of the lower bin, and dump the lower bin contents into the compostable bag. The whole process takes about 3 minutes.

The most recent additions to the toilet will not have fully composted, so it is vital to take care of the solid material properly. You can place the compostable bag in any outdoor pit style toilet in a marine park. Or you can take the material home and place it in your composter, where it should sit for several months. It is then safe to put the fully composted material on non-edible plants. Remember, you only have to deal with the solid waste very infrequently – in sharp contrast to the holding tank approach.

But is it legal?

Yes. Composting toilets are legal marine sanitation devices in coastal (salt) waters in Canada, and all waters in the USA (including fresh water).


Composting toilets are not inexpensive, at about $1200-$1500. However, they are comparable in cost to a more typical marine sanitation system, with a marine toilet, holding tank, two sea cocks, pump, hoses, and a Y valve. As a bonus, a composting toilet will allow you to remove your old holding tank, gaining precious storage space. They are ecologically benign, producing no waste for treatment, and require almost no maintenance. Above all, composting toilets are far more convenient to use, compared to carrying around a sewage tank and planning your travels around pump out stations.

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8 thoughts on “Marine Composting Toilets

  • William H Hanchett

    From your statement about the legality of composting toilets in salt water areas of Canada, I assume they are not yet legal for the fresh water areas such as the Canadian Great Lakes. Is this correct? Is this liable to change?

    • admin Post author

      Transport Canada regulates this. Last I heard, they view composting toilets as Porta Potties, and these are not legal on the Great Lakes. It’s strange, because on the US side, the Coast Guard is responsible for this – and they call the Nature’s Head the “best possible solution”. If you plumb the urine drain to a holding tank, instead of using the urine bottle, it should be legal. I think they are worried that people will empty the urine bottle over the side.

      • Robert Elder

        We live on a boat and plan on cruising in Canada this year. We are still left with the question, is the composting toilet legal in Canada, fresh water? I stalled a composting toilet that gives 2 people about a month of solid storage, and also has the 2 gallon urine bucket. I plan on plumbing the urine to a 50 gallon holding tank that should last us about 100 days. Am

        • Admin Post author

          Your system is perfectly legal in Canada. Marine sanitation is regulated by Transport Canada, and there are different rules for salt water and fresh water. In salt water, composting toilets are legal, no questions asked. In fresh water, it’s a little different. They don’t like the urine bottle with its fairly small capacity, because they think boaters might dump the urine in an enclosed bay or anchorage. There is a lot of nitrogen in urine, so that would not be a good thing. It’s basically fertilizer. So in fresh water they want boats with composting toilets to plumb the urine to a larger tank, as you have done. With only urine going into the tank (and not gallons of flushing water), that tank is going to take a long, long time to fill up.
          All that said, we have never heard of a case of a boater being ticketed in fresh water for using the Nature’s Head with the urine bottle. On the water, common sense prevails. Hundreds of American boats cross into the Canadian side of the Great Lakes every year with Nature’s Head toilets (using the urine bottle), and of course they are never fined. In practice, the only person that is ever going to ask is a marina manager. Your chance of being boarded by the Coast Guard is close to nil, because unlike in the USA, the police or Coast Guard would need a search warrant to board your vessel. I’ve never even heard of it happening.

          • Robert Elder

            Regarding hooking up the urine spout to a hose, I am having trouble finding the right parts to do that. I just spent 1 hour in Lowes pawing over vinal hoses, hose barbs and other what not. Never found the right combination of parts. The biggest obsteical is the urine port, a dia of 1 3/16, an odd ball size. The hose that I found that fits is much to stiff and I am afraid I will break the spout off.

            Would be cool if you could offer a kit to connect to that port.

            How have other solved this problem?


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    • Richard Brunt Post author

      I don’t sell a low water electric model of toilet, so I’m not sure what you are referring to. None of my toilets hook up to a water supply.

      I do not sell a turbo fan. Perhaps you have emailed the wrong company?

      A whirlybird style vent only works where it is windy. If you don’t have enough wind, you need to power the toilet.