There are two main problems with toilets on board: disposal and smell. On land you generally either flush waste away with silly amounts of drinking water, or you have some kind of composting toilet. Space is at a premium on boats so toilets which compost your poo right there are rare, although there are some designs around (see Commercial Compost Toilets below). Unless you've managed to come up with a great design for a true composting toilet then sooner or later you're going to have to get rid of your poo.

While you're getting round to taking your poo off board you don't want it smelling. The smell is caused by anaerobic bacteria - that is, bacteria which survive in conditions where there is no oxygen (eg in an airtight box, or under water - or in urine). Traditional boat toilets and eco-toilets deal with the smell problem in different ways.

Traditional Boat Toilets - Port-a-pottis (Thetford) and Tanks

Port-a-pottis and tank storage systems rely on serious disinfectants to kill the bacteria. ' Blue' usually has a large amount of formaldehyde in it to kill off the anaerobic bacteria. Formaldehyde is a very serious health risk, a known carcinogen and a long term water pollutant. Because it's so dangerous it shouldn't be allowed to come into contact with the skin, or inhaled, or allowed to enter our water courses. But somehow we think it's OK to put it in our boat toilets (and if we can smell the perfume they put in the 'Blue', surely the formaldehyde is finding it's way up our nostrils too?) Disposal of the contents of our port-a-potti or tank at the elsan point or pump-out means we don't have to deal with the formaldehyde-poo-wee mix anymore, but the formaldehyde causes problems to the sewage works too - they rely on bacteria too clean sewage, and guess what? The formaldehyde kills them off...

Thetford's Aqua Kem 'Green' is becoming a regularly available alternative to 'blue', and is made and recommended by Thetford. But the bottles of green don't declare their ingredients either. At the very least we can expect some other strong disinfectant, synthetic perfume, synthetic colourings and other fossil-fuel based nasties.

'Eco-tablets' of various kinds are available - anyone know any brand names, what's in them and where to get them?

BioMagic claims to be a way of activating decomposition naturally. Oxygen and Nitrogen are mentioned but there doesn't seem to be a full ingredients declaration available, and the whole thing is imported all the way from the USA. 

It is recommended by some users though: "I was given a free sample by my BSS surveyor and we have purposefully left our toilet in a minging state (multiple users several weeks without emtying) and guess what? - no smell and evidence of 'natural' decomposition."

"Folks, If I may join the discussion? I'm the Boat Safety Scheme Examiner who provided the sample; I do this with all my BSS customers, in order to spread environmentally sound practice. If you would like to try BioMagic, I'm happy to post to you a half-litre bottle without charge, either for the BioMagic or postage. In the first instance, I'll provide a dozen bottles, if the demand is greater than this, I'll try and provide more. Just get in touch via my website (link below) and I'll do the rest. Best wishes, Andrew Phasey"

BioMagic claims:

  • [It] is harmless to humans and animals, plants and the environment. It does not contain dyes or chemicals, although a perfume is added to aid identification. BioMagic is a natural bio-stimulant, enhancing Nature's ability to break down waste products. Unpleasant odours are produced by waste when natural bacteria, already present, do not have sufficient oxygen to complete the breakdown process. Oxygen-rich BioMagic assists natural bacteria to work more efficiently. Treating waste with BioMagic produces a harmless and odourless liquid residue that can be flushed away without causing harm to the environment."

More info and contact details on the web-site of said surveyor who is the UK agent for Bio Magic at

Yeast - brewer's yeast tablets from your local health food store (has anyone tried baking yeast?). If you're using a porta-potti then yeast tablets seem to be the cheapest and greenest way to go. There have been lots of reports of people using yeast to neutralise odours from your port-a-potti/tank. Just put 4 tablets after emptying the cassette and let it do its job. Take care to flush your tank/port-a-potti thoroughly to try and get as much of the blue out as possible - even then it can take a few fillings and emptyings before the yeast begins to work properly - up to six weeks - so be patient!

Compost toilets

Compost toilets are simple, easy to build, and if looked after, pleasant enough to use.

They rely on keeping the poo aerated (ie not all sludged together so that air can't get to it) which allows bacteria to decompose the waste without horrible poo-smells. The way this is done is by making sure that it's fairly dry, usually by adding sawdust, wood ash or other absorbent materials. Separating the urine obviously helps because you need less absorbent material. Every so often you may need to turn the pile - just like with 'normal' compost heaps - to make sure that air gets to it, and that any pathogens are exposed to the high temperatures (caused by decomposition) in the middle of the heap.

Is Humanure safe?

Talking of pathogens, how safe is human compost? The rules of thumb are:

  • vegan poo = safe to use on your allotment after it's been composted for one year

  • vegetarian (ovo-lacto) poo = safe to use after three years

  • meat eater's poo = safe to use after seven years

Fully composted poo is much like any other proper compost - crumbly, dark, pleasant smelling and safe to handle.

It's common to use humanure compost around trees and bushes rather than on your strawberries - this removes the 'yuck factor' because the humanure compost doesn't come into direct contact with your food.

Just as with any toilet system remember to wash your hands after you go to the bog!

Composting your poo on board

On land, compost toilets and tree bogs are easy to maintain, but on board, where space is limited there is the question of whether to actually compost the poo there, or take it elsewhere (your allotment? a friend's garden?) for the composting process. Your wee is also a problem - put it in with the compost and it makes it a lot harder to keep the compost dry. Remember, if you don't keep it dry then it'll start to really smell! Obviously you can just add a lot more sawdust but this will add hugely to the amount of compost you have to store while it is composting - about 4 to 5 times as much.

[Another way to compost on board is by using wheelie bins if you have the space. See London LILO story for more info]

If you don't want to run out of space then you need to speed up the composting process. The usual way to speed up any composting process is to regularly turn the pile. This is what the commercial composting toilets generally do - see below.

Compost collection systems on board

We haven't heard of any working compost toilet designs on boats (if you know of one please add any details here) - most boaters use a bucket to collect their poo, then take it elsewhere to be composted. This doesn't have to be as basic as it sounds - a nicely designed bench or seat with the bucket beneath can be as attractive as any toilet. Smells are dealt with by keeping the contents of the bucket dry - just add some dry matter, like sawdust, soil or wood ash (not coal ash - these are toxic and you don't want to put these on your allotment or garden!) There's no need to completely cover your poo, just sprinkle a bit over the top. If it begins to smell then use a little more.

When your bucket is full just take it somewhere where you can add it to a compost heap - see building a compost heap below. If you haven't got the possibility of putting your bucket on a compost heap then you have a problem. Some people bury their humanure in the woods, but there are questions about how well it decomposes under these conditions. On the one hand archaeologists are still digging up Roman poo (still soft!), but on the other these faecal remains were probably not mixed liberally with dry matter beforehand - something that greatly aids decomposition!

Another possibility would be to dispose of your poo down the mains sewage system - but you could well block the pipe with all the lovely dry matter from your bucket (not to mention the waste of good fertiliser!)

To separate or not to separate - a wee question

If you don't wee in your compost collection bucket then you can go for much longer without having to empty it (about four times longer!), and you'll use only about 20% as much sawdust. But what to do with the wee? Simply collect it any way you can, and spread amongst the bushes on the towpath. Don't always water the same spot because the nitrogen in the urine will burn the plants - make sure to spread it around. You can also dilute it with 5 parts water and water your plants with it - great fertiliser and easy to use.

Compost collection bucket toilet designs

The general design puts a 5 gallon fermentation bucket (used by wine makers - readily available, cheap, a standard size so easily replaced and big enough for one person's poo for a month, or poo and wee for a week) under a bench or toilet seat. Leave a gap between the top of the bucket and the seat so that air can circulate freely.

If you suffer from smells despite using lots of absorbent material like sawdust you could consider a 'chimney'. By attaching a chimney to the bucket, and through your boat roof you can set up a draught that encourages any smell to go up your chimney rather than into the bathroom.

40mm standard waste pipe makes a good smell chimney and is often found in skips. Because it's a standard size you can get cheap fittings to attach it to a hole high in the side of your bucket. Keep the chimney straight, and paint the top (above your roof) black so that it can warm up and draw better. You'll need to make some kind of rain hat to keep the rain from getting into your compost collection bucket.

Compost collection bucket problems

Smelly - is it it too wet? Or is it compacted? Add more dry stuff like sawdust and mix it in. You could also put the bucket in a warm place to dry out - in the winter this could be in the engine well when you have your engine running. If it's compacted then you'll need to give it a good stir while adding more sawdust. You may find it easier to empty your bucket on the compost heap, making sure to spread it round as you do.

Mouldy or furry - is it too wet? is your dry, absorbent stuff really dry? Do the above, and if your sawdust is damp then try drying it out by putting it in a pan or other on top of your burner. The sawdust shouldn't be too dry, but it shouldn't be obviously damp either.

Building a compost heap

If you already know how to compost kitchen and garden waste then you'll have no problem composting humanure. The same principles apply whether you're composting poo or veg cuttings. Making compost is quite straightforward:

  • Find a way of keeping your compost in a big pile rather than spread out: you can use a compost bin or make a heap with wooden sides about 1m x1m x1m. This means the compost heap gets warm enough to kill any pathogens or seeds, and helps speed up the bacteria that turn the waste into compost.

  • Make sure you're heap doesn't go anaerobic - when air can't get to the compost it turns to smelly sludge. Making sure it's not too wet, and turning it with a garden fork is usually enough. Never press your heap down!

  • Covering up your heap can help too - it keeps it warm, stops it getting too wet in the rain, or too dry in the summer. Now and again you may need to take the lid off because the heap is too dry, or too wet etc. Straw and old carpets are common covers.

Most people keep a separate compost heap just for humanure so that they can compost it for longer and save it for use on trees and bushes rather than ground crops (see the section Is it safe above).

Commercial compost toilets

Commercial compost toilets are available which compost your poo and wee so that you can remove rich, smell free and safe compost after a few months. These cost quite a lot - the Swedish Biolet advertise their smaller compost toilets to the boat market at around £1000!

Biolet claim their compost toilets are also suitable for narrowboats and small yachts. Their smallest model has an electric and non-electric version. The electric version looks like it would eat up quite a bit of energy - it has a 400 Watt heater, and a fan which goes continually in order to keep the odour going up a chimney rather than into your bathroom. There's no information on their website as too how long the heater has to run for, but the fan is likely to be nearly one Amp - so that's about 20Amp-hours per day! Fine if you're on a shoreline or cruising every day...

The non-electric version is scarcely better - not only does it need an 'operating temperature' of 17C (fine for summer, but you'll have to cross your legs all winter) but it relies on a soakaway (ie a pit full of gravel or stones where liquid can soak away into the ground) for urine in order to keep the composting process relatively dry - important to keep odours down. Not too many boats around with soakaway facilities, are there?

The Biolet website does have diagrams of the various chambers in their compost toilets - these are worth a look if you fancy designing your own true composting toilet.

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yeast tabs

we have been using these for abit and they do work, it is best to leave the full porta pot to stand for a few days then empty, gives a better break down Laughing

compost loo

hello, why not use your exsisting porta potti, only instead of using a chemical go to a timber / joinery shop and get a big bag a sawdust for free or a small sum ,and every time you go!, put a small amount on top of what youve done and close the lid and let nature do the rest.ive found that two porta pottis are needed as one can be digesting while the other is in use.

how do you get the composted

how do you get the composted humanure out of the porta-potti when it's all rotted down?

Chemical toilet additives

I tried BioMagic in my porta-potti and found it worked very well; but then I did a comparison experiment where I didn't put ANY additive into the tank and there was little difference... That said, I am quite assiduous about keeping pee seperate and I don't eat meat which may help. Anyone else tried this?

Pathogens in Humanure

Please take the times to be safe using Humanure as what they are: an expression of revulsion by a vegan at carnivores. No problem, but our internal flora are very similar whatever we eat, and there is not a shred of actual evidence that after one year, let alone seven, there is any difference. Please go vegan, but the benefits can be seen without making stuff up.

Separating out the wee

Good thermophillic composting takes place when there is urine in with the 'dry' deposits, allowing the pile to build up enough heat for composting to happen - otherwise, you are still at the 'collecting' stage of composting (fine if you have an on-land compost pile to dump it on). Commercial compost toilets rely on dehydrating the poo, but dessicating the stuff isn't really composting it, is it? Once thermophillic composting starts, the wee is evaporated off anyway, but waste is properly broken down in the process. The big problem with this method is storage space to allow time for this to happen on a boat that is moving around the country. I've shifted a couple of gas bottles out the bow locker to make space for 'fermenting buckets' but dunno if there's enough space to be able to complete the cycle!

Good reading on the subject : The Humanure Handbook' by Joseph Jenkins