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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13 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?


          • Richard Post author

            Typically you put a bulkhead fitting in the urine bottle at the side, near the bottom. It can be any size you want.

  • Tim Kritzer

    There is lots of boating traffic on the Great Lakes of course…
    Fishermen typically use a bottle for urination and just dump it over the side… For purpose of discussion then – considering they are off shore… is this considered illegal in Canadian fresh waters – the Great Lakes…?
    I have a sailboat and am just off the washrooms when tied up – urine could be offloaded then safely there…
    I typically sail off shore in Erie a couple of miles out, and am very much further afield cruising… whether it amounts to any consideration… I’m single handed 95% of the time.
    Can I legally, when sailing off shore in open water, dump urine into the lake (Erie)?

    • Richard Post author

      Excellent question. There is a lot of misinformation online about this. I have personally done a bit of research on the topic. It is actually illegal to pee in a bottle and dump it over the side in the Great Lakes, on the Canadian side – even though huge numbers of people do this. According to what I was told by Transport Canada representatives on the phone, you can pee over the side – that is legal, but if you pee in a bottle and dump it over the side, that is illegal. Clearly, this is insane, but that is our federal bureaucracy working its magic. Therefore, Transport Canada doesn’t want us dumping the Nature’s Head urine bottle over the side on the Great Lakes. (To be clear, it is perfectly legal to dump it over the side in salt water). The solution is fortunately easy. You plumb the urine bottle to a larger holding tank. (I can provide guidance on this). This tank will take a very long time to fill up, since it’s just pee and no flush water. Then you would get rid of the urine at a pump out station.
      Thankfully, on the water, sanity prevails. To the best of our knowledge, no one has ever received a ticket or warning about using the Nature’s Head as designed – with a urine bottle. The marine police are thinking a lot more clearly on the topic than our government officials.
      The reason given for not dumping a bottle of urine overboard is that it is pretty strong fertilizer. It’s a valid point. However, I have a hard time understanding how a few gallons of pee are a concern, when millions of gallons of fertilizer-laden and pesticide-laden agricultural run-off enters the Great Lakes annually.
      Also interesting is that, in US waters on the Great Lakes, the US Coast Guard calls the Nature’s Head (and similar toilets) “the best possible solution for the Great Lakes”. Hundreds of boaters from the US sail with their Nature’s Head toilets into Canadian waters every year. There has never been an issue at customs or at any inspection.
      Does that help?

      • Tim Kritzer

        There are a few parts I guess to my considering a composting toilet.
        I love the idea that I can very likely, as a single handed sailor, stretch a toilet refurbishment out for the whole season… it really is just an emergency backup for me anyway, as I’m never far from tying up somewhere for the night – at this point I do very little gunk-holing…
        Then of course, I would require a sanctioned option on board.
        I like the idea of shedding the maintenance of a conventional head – hose replacement, pump maintenance, holding tank pump out, open sea cock.
        Ease of use for guests on board is a courtesy I would like to extend – remedying someone’s dilemma after the fact is an embarrassment for all involved…
        Primarily though – I want the stowage room back that I now forfeit to the holding tank…
        I get the point being made in shore off loading urine – but it seems of course a hand over played, as we all know what does happen out on the water anyway… and of course – who has ever gone swimming and not exercised the opportunity to drain and rinse…
        A two gallon container attach, with a spare at hand … you’d think would satisfy the authority…
        Wanting of course to do the right thing, but present practise by and large seems to fly in the face of joining reason between existing and common practise and regulation…
        I’m likely to proceed, but my ‘holding’ tank now will go, and I’ll throw myself upon the validation of sciences with a much smaller two gallon back up bottle… and forgo the 30 gallon tank I now have but so rarely use…
        I want to convert my motive power to electric when sails are down – I want the coveted space for battery bank…
        Trying to catch up to the 21st century with a 20th century boat…
        Thanks for your guidance, albeit, I am going to deviate from it slightly – my bad:)

      • Georges Peron

        From the posted comments Transport Canada regulations for Canadian rivers and lakes, composting toilets require a plumbed holding tank to be connected to the urine Bottle to be legal.
        I am hesitant to buy a Nature’s Head without detail instructions on what is needed (parts & sizing) to connect a urine bottle to an existing or new holding tank.
        I would appreciate reading how this would work!
        Currently, the existing holding tank is very small (10 to 15 litres) and is higher than the toilet seat.
        Thank you

        • Richard Post author

          It is a DIY modification. The manufacturer does nor support it with parts or advice. I can’t tell you the exact parts, or what you need for your unique installation. Basically however there are two ways. You can connect a flexible drain hose to the urine drain spigot. Or drill a hole in the urine bottle, on the side near the bottom, and install a drain hose with a small bulkhead fitting. You pretty much need to be confident figuring it out from there. You do need gravity, or a pump.