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Separator (composting) toilets

Separator (compost) toilets have become increasingly popular on boats over the last few years.

This is partly due to environmental concerns as well as simplicity of use and lack of access to facilities such as Elsan or pumpouts.

The increasing number of boaters with separator toilets, with no means of composting, has led to an increased use of binning the solid contents in Canal & River Trust waste bins. This increases the risk of cross contamination of other content, which is otherwise sorted and mostly recycled, and can result in the whole bin being sent to landfill.

This is not an environmentally sustainable way of disposal. There is a need to find alternative ways of dealing with solid waste, and composting is the easiest solution.

Frequently asked questions

What's the difference between a separating toilet and a composting one?

The term 'composting toilet' is misleading as the toilet doesn't do any composting. It's something that has caused a lot of confusion since interest in non-water based/flushing toilets began.

All toilets are simply collecting units. In water-based systems it's a funnel into a cassette or a pump out tank. In a composting system the toilet separates urine and faeces into separate containers for processing and disposal. A separating toilet is part of a composting system.

It is not as simple as buying a different brand of toilet, so planning to manage the composting and disposal stages is essential.

How does a separating toilet work?

Separating toilets on boats divert urine deposits into a container which can then be taken to the Elsan or watered down and used on land as fertiliser. Solids are collected in a separate container, with or without toilet paper included and covered with an additional material (often wooden cat litter or sawdust) to help keep the contents dry.

Once the solids bucket is full the contents need to be moved into a secondary location where the actual composting happens. No composting actually happens in the toilet unit itself, it's simply a collection unit.

Why not use the existing pumpout or Elsan?

If disposed of in the Elsan, solids from separating toilets would block it due to their dry nature as sawdust or other material is added. Elsan and pumpouts are expensive to repair.

How do I process the solids?

Once the solids container is full the contents need to be moved to a final container to complete the composting process. This is essentially a very simple process, where the materials are given the best possible environment to decompose.

Composting needs a mixture of materials: moisture, oxygen, and time. The result is a useful soil addition which provides nutrients for plants and is good for soil health and the many organisms which live there.

Where do I process the waste?

The contents of a separating toilet can be added to a garden compost bin, or, if you are short of space, a smaller container. Generally, composting works better in a larger container.

What does a hot bin do?

An insulated composting bin such as the ‘Hot Bin' will speed the process up. A hot bin is said to break down all food and waste in three months.

What about bacteria?

The early stages of composting will inactivate most bacteria, although it is always advisable to wash hands after handling any compost and avoid getting it into open wounds or eyes. This is only part of the process though. The microbes will carry on breaking down the material long after any bacteria are dead. Once fully composted it will be dark, crumbly and earthy smelling.

How long does composting the waste take?

The World Health Organisation recommend two years to compost humanure. However, their guidelines are for any community in any country worldwide. In practice, many people in the UK who are composting just their own toilet material achieve a good compost in half that time.

What do I do with the finished product?

Once the composting process is completed, the compost can be used in a garden. Many boaters mix it with older compost or soil and use it in cabin top flowerpots.

These FAQs were prepared with input from boaters Kate Saffin, Helen Rose and Master Composter, John Cossham, all of whom have a composting toilet system.

A more detailed guide to the process of composting humanure by John Cossham can be found at started as a group for boaters but now has an international membership living in a wide range of off grid settings. It has a comprehensive collection of files covering the science, evidence and practical management of separating toilets and composting. is a new group specifically for UK boaters who are just starting out or researching composting. Membership includes boaters without a home mooring composting on board as well as those with land to set up their system on.

The Humanure Handbook by Joseph Jenkins provides all the theory you will ever need. He doesn't use a separating system, but it is still a very useful read and contains valuable information on the common concerns, such as how long pathogens survive. The 3rd edition is available online as a free PDF download, but it's well worth considering buying the 4th edition as a lot of the content has been updated.

Separator toilet manufacturers - the UK dealers for Separett and Airhead

Last Edited: 18 March 2024

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