What is a compost toilet?

Want to understand more about compost toilets?

This information relates to Separett & Air Head urine diverting compost toilets. For Kazuba, please click this link as the workings and management is fundamentally different.

In this section, we’ll attempt to explain the basics of how the Separett and Air Head compost toilets work, help you understand the differences between the models, so you can choose the right one for you, and go on to explain their day to day maintenance. Please explore the other sections in the Help menu for more information, and if anything is not clear, do get in contact!

Remember that a compost toilet is a part of a whole system – the other key part being a compost bin or place where the composting takes place. The toilet is essentially the collection system for the raw ingredients that will be completely broken down and made safe by the composting process. Keeping the collection and composting separate means that the compost toilet can be simplified – and simple is good! Nothing mechanical to break, no big energy bills and a nice compact toilet that doesn’t take up much space!

Unlike Separett and Air Head, other brands of compost toilets that try to do the composting and/or drying within the toilet are a) typically much more expensive, b) more liable to break down due to the complex nature of the agitating and heating, c) more expensive to run and maintain and d) physically much larger due to all the extra components.

Easy management is all about separation!

The key to a low-maintenance, simple compost toilet is keeping liquids (urine) away from the solids (faeces). This keeps maintenance and odours easy to deal with and emptying less frequent.


When you mix urine and faeces together, you get ‘blackwater’ which will quickly become smelly as things start to break down in the absence of oxygen. You could use a simple bucket system (to collect wee and poo) and add a lot of sawdust (as a cover material/odour control) but having somewhere to store and then compost the contents means you’ll need a fair amount of space and a fair amount of time to manage it. If you want something that needs less maintenance, and is far more elegant, read on…

We believe the key to a compact toilet is to separate the wee from the poo at source and deal with each one individually. This is where the urine diverter or urine separating bowl comes into play…

It works on a simple principle – when you sit down on the toilet, urine will flow to the front and faeces will drop down towards the rear. It doesn’t matter whether you’re male or female, it works the same as long as you sit down.

The separator is specially designed and has a front part to capture and direct the urine, and a chute towards the rear that ensures solids go straight down into the container below.

Separett developed their urine-diversion separator back in the early 1980’s and have refined it over time to end up with the best on the market. The Air Head uses a similar approach but in a slightly more compact format, due to it’s nautical origins.

Where does the wee go?

For Separett toilets, if you’re on land, then the easiest and simplest option is to run the urine into a small soak-away pit (aka leachate drain). We have a section covering soak-away pits in more detail, but essentially it’s a small hole in the ground, filled with gravel, hardcore etc into which the urine will run. The large surface area of the gravel/hardcore slows the flow and enables naturally-occurring soil bacteria to feed off the nutrients in the urine and render it harmless. Any excess liquid will gradually and slowly dissipate in the ground.

A properly made soak-away doesn’t require any maintenance and it doesn’t smell. It’s a simple and effective solution for permanent and semi-permanent land-based installations.

Urine, also makes a great fertiliser due to its high nitrogen content, so some people like to capture it, water it down and apply it as a feed to their garden… Separett make a product called the Ejecktortank which can store up to 50 litres of urine and connects to a hose pipe, enabling the correct dilution for feeding your garden.

With the Air Head, there is a 7.5 litre container on the front of the toilet into which the urine will run. Every day or so, depending on your usage, this need to be emptied.

What about poo?

Because of the separating design of the bowl, poo or solids will drop down into a container within the toilet. In Separett toilets, this container usually has a biodegradable liner for ease of handling. With the Air Head, the whole base of the toilet is the solids container, and because it uses an stirring mechanism, a liner is not used.

Because it’s just poo (and toilet paper), it will be fairly dry and the volume is likely to be much less than you might expect. In addition, it will continue to dry out, further reducing the volume over time.

If you are a DIY enthusiast and building your own compost toilet using the Separett Privy 500 or 501, then one of the simplest ways of dealing with odour is to use wood shavings or coarse sawdust as a ‘cover material’ – all you do is cover what you’ve done with wood shavings (a handful or two is usually enough) and that’s it. Wood shavings are commonly sold in small packs as pet bedding, and are slightly coarser than pure sawdust (which is too fine) and work as a biological cover, enhancing the subsequent composting and reducing odours.

If that sounds a bit too rustic and not your thing, then you’ll be pleased to know that the Separett Villa has a built-in fan that removes all odours and does away with the need for a cover material (no sawdust required at all). The Air Head toilet also has a fan that take care of the odours.

The Separett Villa (2022 model onwards), Separett Weekend and Separett Tiny toilets can power the fan either from a 12V battery (great for off-grid use where you have a solar panel for example), or from 230V mains with the supplied adaptor. The Air Head has a 12 volt fan, making it ideal for boats, narrowboats, caravans and camper vans.

How long the solids container lasts before needing to be emptied depends on a number of factors – the number of users, and how much toilet paper you use… As a rough guide, the Separett Villa or Weekend solids containers would last a single person between 6-8 weeks if they didn’t use any other toilets, the Tiny around 7-10 days, and the Air Head is around 4 weeks.

So that’s it – now you know the basics of how a waterless urine diverting compost toilet works! You just sit down, do what you have to do, and go! Simple, effective, minimal moving parts and very low power consumption.

Not sure which toilet is right for you, need a quote or want to know a little more information?

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