A Quick Guide to Composting Toilets

If the average person flushes the toilet six times a day for a year, that’s 2,190 flushes a year, give or take. Each flush uses two gallons of treated water, which means 4,380 gallons of water are wasted every year.

There aren’t many painless solutions to this. So many areas of our lives rely on modern technology, and finding ecologically-friendly solutions takes real commitment.

In the bathroom, at least, there’s a way to minimise your environmental footprint. A composting toilet is a sustainable alternative that lets you live small or off the grid.

What is a composting toilet?

Also known as a “humus closet,” a composting toilet turns solid waste into compost. There’s no difference in how you typically go about your business in the bathroom. But instead of flushing your poop with water, you “flush” it with organic matter like sawdust or coconut fibre. There is no need for water, pipes, electricity, chemical cleaners, or sewage treatment.

The original toilet was a hole in the ground, and excrement (from humans and animals) was left in the ground to decompose. The composting toilet is simply a refinement of this fundamental process.

A composting toilet decomposes solid waste like you would compost kitchen scraps. Aside from producing nitrogen-rich fertiliser, using a composting toilet is a more sustainable way to live on a struggling planet.

How does a composting toilet work?

A composting toilet has two chambers. The first chamber is in use, and the second chamber is left full so that its contents can decompose fully. Every few months to a year, the second chamber is emptied. Plant matter (like weeds and vegetable peels) is added to the first chamber, which begins its year of decomposition.

1. Use the toilet

Human waste is deposited into the composting toilet much like any regular toilet. But instead of flushing it with water, you flush it with “soak.” Soak is a scoop of carbon material — such as wood shavings, straw or hay, coconut fibre, or dead leaves. This gives the bacteria in the toilet chamber a generous supply of carbon and nitrogen. Without the soak, the bacteria would anaerobically (without oxygen) digest a nitrogen-rich diet, resulting in nasty-smelling ammonia, hydrogen sulphide and greenhouse gas methane. But with the correct quantity of soak, the solid waste is decomposed aerobically (with oxygen), resulting in the generation of nitrates, phosphates, and sulphates — i.e. fertiliser!

2. Waste mixes with organic matter

Liquid and solid waste are separated. The liquid is evaporated, and the solid waste falls into a chamber that has organic matter to bind with. Composting toilets need to stay moist, not wet. This is done by separating the liquid from solid waste with a diverting piping system or container.

3. Aerate

Waste and organic matter are mixed using a rotation handle on the composting toilet. Microbial activity and oxygen in the chamber cause the temperature to go up, killing toxic pathogens. Bacteria, fungi, worms, and other microbial organisms break down the solid waste elements into compost.

4. Odours are vented

Odours and gasses (created by the evaporation of liquids and chemical change of solid waste) exit your home through a vent pipe. Some composting toilet models have a solar-powered fan fitted into the vent pipe and automatically activated when the toilet seat is lifted. A drain at the bottom of the chamber pushes out excess liquid to keep the container dry.

5. Remove composted waste

Remove the composting bin and use the compost to fertilise trees and plants. The compost will look and smell much like the compost you expect from a garden compost pile. Even if there is a little odour, it can resemble the smell of mulch or wood.

Composting toilet vs. standard toilet

With standard plumbed-in toilets, excrement is dumped into a sewage system that carries it into treatment facilities, where the waste is cleansed of toxic elements. The “clean poop” is then released into waterways and the ocean.

For many communities, septic tanks are the go-to solution. But septic options are expensive, heavily regulated, and difficult to maintain. If something goes wrong with a septic tank, it can be catastrophic. On the other hand, if something goes wrong with a composting toilet, it will simply be a smelly mess.

The majority of composting toilet models are built to last for years — a waterless way to dispose of waste needs fewer components, which means fewer components will potentially break down.

Types of composting toilets


A self-contained composting toilet houses the entire composting system, usually beneath the bowl itself. These toilets are generally found in RVs, boats, or tiny homes. A self-contained toilet typically needs to be emptied by hand.

Central or remote

This type of composting toilet brings solid and liquid waste to a central composter located elsewhere on the property, usually underground or outdoors. A wide central network can connect multiple toilets, ideal for large households or compounds.

More recent composting toilet models have innovative bells and whistles such as automated control and synchronisation. The use of electricity can also speed up the composting process.

Not sure which one you need? Read this

How often does it need to be emptied?

Some composting toilets need to be regularly cleaned, but some can be left alone for more extended periods. 90% of human waste is made of water, which evaporates quickly.

Since the solid waste in composting toilets doesn’t go into sewers or septic tanks, the toilet needs to be emptied every few weeks to a few months — depending on how often it is used and how many people use it.

How much does it cost?

On average, a composting toilet costs around $1,500. This may seem like a lot of money for a toilet. Still, it’s cheap compared to other off-grid systems such as septic tanks.

Do I need to get council approval?

Yes. But before anything else, you will want to make sure that the composting toilet you’re considering meets Australian standards. In 2004, new state approvals required composting toilets to be certified to New Zealand and Australian standards AS1546.2. This particular standard is part of a series revised for both Australia and New Zealand for on-site domestic wastewater management.

Your local council plumbing officer will know the regulations for getting council approval. This usually involves having a geotechnical engineer conduct a soil test and draw up a site plan. If your toilet is state-approved, the council will likely be more interested in what you plan to do with your greywater than with your toilet.

Council approval specifically for NSW and Victoria

If you’re considering a composting toilet for your Mod, please contact our team so we can custom-install it for you.

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