In which I talk about toilets.

Every boater’s favourite subject.

Wait, don’t go. You know you want to know how I managed to go three weeks without emptying a Thetford cassette, despite daily use. Don’t you?

Emptying a cassette toilet has to be up there in the top few manky jobs that have to be done on a boat, along with emptying the bilge. I’m not especially tittle-stomached, but the smells and sounds that come from the sluice when performing the necessary duties turn my head. I also dislike the idea of having to cruise to an elsan point every few days and having to pay money for Blue/Green. So I came up with the idea, based on a little research, of separating solids and liquids. I will be discussing solids and liquids in this post, so if you’re squicked by such things, please don’t read any further. You are going to learn some things that perhaps you don’t want to know.


The majority of human output per day is liquid. Average output is between 800ml and 2 litres, which will fill a 15 litre cassette quite quickly, especially if there are two or more people using it. There is some liquid in the solids, but much less. Add in the flush water, and you’re in the situation of having to empty the tank every few days. This costs time, money in the form of having to buy additives like Blue/Green and also increases the amount of dealing with sh*t in your daily life. Who wants more of that? Not me.

The setup I currently have involves two containers. I’m using a standard Thetford 365, with a 21 litre waste tank, for solids, and a 20 litre adapted bottle for liquids. The Thetford sees use on a daily basis, with Green in the waste tank and Pink in the flush which is used each time to clean the bowl. The adapted bottle also sees use on a daily basis and collects as much liquid as possible. I’ve tried various permutations of collection bottle, varying from an inverted 2 litre pop bottle sellotaped to the opening as a collection funnel, to my current setup, which has a 5 litre collection funnel attached to a pipe which enters the tank and is adjustable in height. This bottle has 2 tablespoons of sugar added every week to remove the smell. They sit side by side in my bathroom and take up hardly any space between them. I am lucky enough to be anatomically designed to be able to use such a setup with ease, though it’s quite possible that it could be adapted to suit those of us who aren’t blessed in an appropriate fashion.

As mentioned, the cassette has Green in it. As I mentioned, I use sugar in the liquids bottle, an idea I picked up from composting toilets, as it’s much cheaper than other products and works very well. In the interests of science, I’ve had a good sniff of the contents of the bottle and while they weren’t completely scent-free, to put it in perspective, emptying the cassette is a MUCH more unpleasant job. The bacteria in urine are different to the bacteria in faeces, and adding sugar helps cut down on the ammonia smell hugely. In keeping the two separate, it also leaves the bacteria in the green with only one kind of bacteria to deal with.

I started May with an empty cassette, apart from the manufacturer’s recommended dose of Green, which is 100ml per 10 litres of holding tank. I used 200ml for a 21 litre tank. I had to empty it twenty four days later, after normal daily use. I gave the tank a good shake before emptying at the sluice (remember that I’d been using the flush so there was sufficient liquid to allow easy extraction), which went about as well as dealing with a box full of excrement ever can. A shake of the tank every couple of days is also useful to help keep everything nicely mixed and assist with the breakdown. There was a smell produced, but as it wasn’t the smell of urine AND faeces, it wasn’t as offensive, or as strong, as usual. This tank contained my complete output for the past 24 days. I was expecting to be retching, but it was a lot less unpleasant than I expected.

Dealing with the liquids container was also quite easy. I decided to empty this at the same time, even though it wasn’t completely full. I have been using facilities elsewhere, such as supermarkets where convenient, for ad hoc disposal of liquids. Adding the sugar on a weekly basis seems to have worked very well, as there is very little smell. A bag of sugar can be purchased for about 70p and will last me several months, saving me a fortune on Green. The collection funnel is “flushed” after each use using a spray bottle of Pink, diluted to a litre of water and a quick squirt of Pink. This method of collection is very similar to that which is used in composting toilets, newer varieties of which separate solids and liquids.

The first iteration of the liquids bottle was quite simple – a 20 litre bottle with the lid removed forms the base and a standard 2 litre pop bottle formed the collection funnel. The bottle was inverted, with the opening inside the larger opening of the collection bottle. With the “shoulder” of the smaller bottle resting on the larger bottle, sellotape was wound round to hold it in place. The base of the pop bottle was cut off to allow access and a ping-pong ball was used to form a simple valve. This would float on the surface of the liquid and allow it to drain, but also come to rest on the opening of the bottle and prevent any smells. This was quite serviceable, but there were some problems. There was no facility for height or angle adjustment – one had to be in the correct position before use to ensure collection, and having sharp bits of plastic pressing against one’s genitals is not my idea of fun. Also, I wasn’t convinced that the sellotape would hold long term, and it would have to be completely replaced every time I emptied the bottle.

The MkII version has the same 20 litre waste container as before, but the lid is screwed in place. A short section of 40mm standard waste pipe (the kind you have on a bath) passes through the lid and enables the collection bottle to be raised/lowered to suit. A 5 litre water bottle has had the base and one side removed, creating a much larger access area, which is then inverted and inserted into the top of the pipe. A ping-pong ball completes the valve. At all points, as the liquid is obeying the law of gravity, joints are made downhill, like the tiles on a roof, so that liquid won’t rest on any surface. As before, I’m using a 1 litre pressure sprayer to provide the flush. This model also doesn’t smell, as I’m adding the same amount of sugar as before. I love the fact this model can be adjusted to suit my height and it has a much larger collection area, which is always useful.

All in all, I’m pretty pleased with this setup. It does take up a little more room, but it greatly reduces my visits to the sluice and saves me more money.

How do you … do?

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