Monday, 6 February 2012

A radical toilet

The original toilet.
The toilet that was installed when I bought the boat was awful. It was badly installed, but other than that, it was the usual bit of kit. The toilet itself was a Lavac, which uses seawater to flush, and it could be made to flush directly into the sea or into a holding tank. The holding tank could be pumped out either into the sea or out via a deck fitting to a pumpout in a marina. These pumping options were provided by one pump, 2 three-way valves and miles of piping. Have a laugh:

Sorry, it may be a little confusing. I took this photo before I had the idea of the blog. I didn't think much about photographing it through a dirty mirror. Anyway, it gives an impression of 'before'. Not quite the whole picture though. Notice the brown area I've labelled 'bulkhead'. Behind this area was the holding tank, which was kept in place by being embedded in expanding foam - the builder's variety I'd guess. A water heater that had been installed above this area had leaked around the chimney, and the water had saturated the foam. Quite a stinking mess to remove! This had penetrated the bulkhead, causing it to rot. That brown area you see is where I have replaced the lower half of the bulkhead with a piece of epoxied ply.

What's wrong with the usual system?

Through hulls. Through hulls are holes in the boat, and I prefer not to have holes in the boat wherever possible, but especially below the waterline. Through hulls need regular servicing - taking apart and greasing. Otherwise they'll become seized or just leak. I thought my through hulls were OK. When I decided to remove the original installation, I got as far as removing all the pipes and an urgent phone call took me off the job. A family crisis kept me away from the boat for a month. When I got back to it, the port hull had over a foot of water in it. One of the through hulls had had a slight leak. You never know if your through hulls will leak or not until you need them not to! Anyway, I got back to work with more certainty that removing all this stuff was the way to go.

Storage. How big does a holding tank need to be? The bigger it is, the less frequently you'll have to move to go and pump it out. On the other hand, valuable boat space is wasted, and you are storing a whole lot of unpleasantness. My holding tank had been empty for 5 years so I didn't suspect it was the source of a sulphurous smell at first. But that was where the smell was coming from, despite the tank being vented through a carbon filter, and all the pipes being in good condition and tightly attached.

Complexity of plumbing. My setup was very similar to this, but I didn't have the LectraSan electric pump. And I had one extra 3-way valve. But you get the idea.

It's complex. All those pipes, valves, tanks, and sea-cocks amount to quite a bit of expense and weight, something we're always trying to reduce with a multihull. And you don't want any of it to leak. And that deodorant is smelly in itself. Maybe a carbon filter is better, but it doesn't last that long, and doesn't retain all the smell.

Liability to blocking. Dealing with leaks is a bit unpleasant, but once you've found the leak, you might get away with fixing it just by tightening a jubilee clip if you're lucky. There's not much luck involved in dealing with blockages. I once spent a day prising apart a toilet pump in a Lavac system to undo a blockage, and then replacing the valves (which needs doing periodically because the rubber valves harden and become less efficient) only for a new guest on the boat to block it up the next day with a tampon. I hardly knew the woman - getting down and dirty with her used tampon wasn't a good start to our acquaintance.


Porta Potti.
No plumbing involved. Some unpleasant chemicals, and a requirement to empty it fairly frequently. If you go this route, you need a way to fasten the thing down in the boat. I've had the most unpleasant experience of trying to do my business at sea at the same time as trying to stop the thing I'm sitting on from sliding around on the floor. No way you can read the paper under such conditions.
Here's a model I like because of its name:

Thetford Porta Potti 165 Elegance :)

A bucket.
Again, no plumbing involved. It's easy to build into a small cabinet that supports a seat. I went for this option on my last boat, but you need to empty the bucket right away. Not good at all in harbour. Which means in port, you've really got to get over to the harbour facilities to do what you need to do.

A compost toilet.
All the rage these days. Sailing forums are full of people delighted with them, and saying they'd never go back to the old system. The catch? The price.

However, I'd been through this loop before, considering a composting toilet for a small room in my house. Commercially available compost loos are expensive. Then I came across the Humanure handbook. And once I'd read the book, I built this:

and we've been using it now for three years. No problem at all. People prefer it to the normal toilet. It doesn't smell. And produces excellent clean compost we use on the garden including the vegetable beds and even the houseplants! As it happens, I did get a degree in microbiology a long time ago, so I am aware of the possible dangers, but anyway, our composting arrangement works just fine.

But never mind the compost part. We're talking boats, and we don't want to produce compost. We just want to get rid of the waste. Cleanly.

Something that struck me when I built the toilet in the house was how amazingly efficient damp sawdust is at removing smells. Dry sawdust doesn't do it. But damp sawdust works amazingly. A thin sprinkling is all that is needed.

Still, my domestic system is basically a bucket where you sprinkle sawdust over your leavings. Everything goes in, solid and liquid, and that mixture happens to produce the right carbon/nitrogen mix that causes the stuff to really get hot (and kill the pathogens) on the compost heap. We don't want that on a boat. Really, we could do with getting rid of the liquids - they could go straight overboard (because it is basically sterile anyway). There are some compost toilets work that way, like the toilets made by Separett.

Something that surprised me was how complicated some of these toilets are. Some have screens so you can't see the contents - when you sit on the seat, the screen moves away. Some have handles that turns a mixing paddle so you can stir in your latest contribution to the old stuff. And they have extractor fans that continually draw air through the toilet and send it outside.

I'm not squeamish. I can manage without a screen. And I don't believe there's any benefit in turning the mix. People have an idea that compost needs turning (and also that lime needs adding). It doesn't. My heaps compost down to a fine black tilth without any turning or additives (the explanation is in the Humanure book). So what is this business about turning the mix inside the compost toilets all about? I think it's about nothing more than pandering to that mythical requirement, that what you need to do to compost is turn it. I think it works at a psychological level. If you mix it, it must be compost. Because you don't mix poop. And the mixer adds complexity to the whole thing - it puts you off the notion of... making your own! After all, take away the screen bit, and forget about the mixer, and what are you left with? A seat, a container and a fan.

A seat that sends liquids down one way and solids another is available on ebay. £28.89 plus postage. Quite a bit for a simple piece of moulded plastic. But it does the job, and I don't know of anything similar and didn't fancy trying to make my own. A container? A bucket, of course. And a fan? I found 4 in the attic - 12v fans ripped out of old computers. Nice and quiet. And the one I have now installed uses 0.15 amps. No problem. (Since I installed that fan, I found yet another, but this one was attached to a variable resistor - a speed control. I regret missing the option of installing that one, so that when you are using the toilet, you can turn the fan up to high speed when necessary!).

A further thought before I go on to describe my current installation. If the liquid is kept separate and the poop just sits there on a bed of sawdust with air continually drawn over it, it isn't going to compost, it's going to dry out. Poop is usually 75% water. If that is evaporated away, you don't have any issues with weight. Or smell. Ever seen those mummified dog turds in summer? They don't look nice, but they don't smell either. Most of the bacteria are killed by the drying. Most of the rest become dormant as they dry out, sometimes becoming spores. That's not entirely safe to handle, but since it is bacterial activity that produces the smell, when they become inactive, there is no smell. (Sorry, it's the microbiologist in me!)

I think those waterless compost toilets aren't compost toilets at all. They're more desiccating toilets. So I worked out a simple way to improve the dessication.

The new installation.

OK, two buckets, but still, it's not that complicated! The inner bucket has lots of small holes in the base to allow air to pass through. The outer bucket is connected to a standard 40mm waste pipe - cheap, and the bends and fittings are also cheap and easily available. The pipe leads to a small box attached to the top of a small lateral bulkhead that separates the heads from the anchor locker. A 12v computer fan is housed in there. In the anchor locker, the pipe leads down to a hole in the bottom of the anchor locker.

Before using the toilet, sprinkle a thin layer of sawdust in the bottom of the bucket, and afterwards and just enough sawdust to cover your deposit.

So how does it work in practise? Much better than anticipated! The fan continually sucks air down the inner bucket, past your deposit, through the sawdust and it is vented outside. Not only doesn't the toilet smell, but it doesn't even smell while you're using it! Currently I'm working on the boat, so I'm not there all the time, and I don't have the solar panels connected up right now. So I switched the fan off, I expected a bit of a whiff when I got back, but there was none! I realised that even without the fan running, the air passing under the bridgedeck sucks air out through the outlet anyway. You only need the fan when there is no wind at all. Any wind is enough to create suction over the outlet courtesy of Mr Bernoulli so that the smell is taken away continually. Turns out the fan is an optional extra, used only when you want to entirely eliminate smells on days when there is no wind.

Liquid goes down a tube into a 4 litre bottle, and this is easily removed to be emptied over the side, or more discretely, through the cockpit drain.

Downsides? Well, I've only tried sawdust, which I have anyway by the trailer load for my house compost toilet and my chicken house. Separette says to sprinkle soil over it. That might work. I doubt sand would be as good, as it might be too fine to allow the air to pass through easily. Seaweed might be OK. Anyway, I'll take a big bag of sawdust with me when I start out and see how we go. I have a LOT of locker space (because I kept the big fish lockers in the cockpit) and I don't mind filling them up with anything that is light weight. I don't think it'll be a problem.

When the bucket is full, it can be emptied into a bin liner and later be disposed of out at sea. At home, I'll bury it in the middle of my compost heap, where the heat will kill most of the pathogens, and the composting process will deal with the rest. It'll be ready to use on the garden in 2 years (or 3 years, just to be sure, if the heat didn't consistently build up to 60 degrees C). A bin liner, which is several buckets full is still light to carry - just as light as a bag of dry sawdust, which it mostly is.

So far, I'm very pleased with my toilet setup. It cost around £40, and will never leak. All parts are easily replaceable. And the toilet is now where the holding tank used to be (quite a bit of room under the lid for a few bags of sawdust) - which leaves even more space available for washing or taking a shower. Not a bad bathroom/toilet for a 9 metre boat!

A little more painting around the floor and a bit of titivating, and it'll be job done.

a cheap marine composting toilet


After 4 months cruising with the toilet in use all the time, I can report that finding suitable material besides sawdust is easy. Pine needles, dried sea-grass from the beach, leaf mould - anything organic that can be used to cover the solids and allows the air to pass through is fine. A bucket of such material can last a month.

But I have had problems with smell - pretty mild, but noticeable. The smell is usually under the bridge-deck, and is only noticeable when tying up the dinghy at the back. That could be acceptable,  but it's no way to greet a guest. And sometimes, fluky wind blows the smell from under the bridge deck into the front window if it is open. The answer I'm sure, is activated charcoal. The obvious place to put it is in the space between the two buckets. I haven't found any yet on my travels, but the problem isn't urgent.

Other than the occasional smell, the toilet is working out better than anticipated.

Even later:

I have found some activated charcoal at last (pet shops, used as a filter medium in fish tank filters). It was too expensive and the packet too small for me to put it in the space between the bottoms od the buckets. So I put some into a thin sock, and dropped it down the air pipe. Now, there is no smell at all! The air flow through the system is less than it was, but still sufficient. The charcoal I have used this last month is still in place, and completely effective - so my little packet could last for years.


  1. yes....just not sure about the 4 liter bottle of shxty piss water to be continually dumped over the side....make sure you're upwind and all that...4 liter capacity will need to be dumped often I would think....still, the old way is ridiculous! So good on ya.

    1. You're right - the bottle was a pain. And worse when I forgot to empty it and it overflowed. It would be better if the piss-pipe could lead directly to an above-water level through hull, but I don't have the height available for this arrangement. So we have changed our habits a little, and when we just want a p, we use a small bucket, which is promptly emptied into a funnel fitted into the cockpit drain - so we can do that without getting wet when it is raining. This arrangement means the bottle keeps its contents longer, and that starts to smell, unless you add a teaspoon of sugar to the bottle whenever it is emptied and cleaned. I'll post again when we have a perfect arrangement!

  2. Please indicate how the urine is collected in the toilet and into a bottle

    Thanks in advance,

    1. I use one of these:

  3. This comment has been removed by a blog administrator.

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