what is a composting (flushless) toilet and how does it work?

How do composting (waterless) toilets work?

Composting toilets are an amazing way to save money while reducing your impact on the environment. Here, we explore the natural processes at work in a composting toilet, as well as the components which make it all happen with ease and without odor. 

How does a composting toilet work?

Kinds of composting toilets

Before digging into the detail of how does a composting toilet work, it’s important to understand the differences between the main kinds of composting toilets that are on the market so you can see what is the best composting toilet for your situation

Traditional composting toilets

Dating back from the original outhouses and pit toilets, these come in a variety of shapes, sizes and complexities, but essentially are a big hole that you poop and pee in! 

There are some clear disadvantages when compared to modern composting toilets – the smell, the size of the hole required, and the risk of trouble in flood prone zones.

Active composters

Also known as self-contained composting toilets, active composters contain a larger storage unit than dry flush toilets. Solid waste is directly composted in the storage unit. The owner will need to put some effort into maintaining the right conditions for composition, such as adding a carbon material like coconut coir to encourage aerobic processing, and microbial starter cultures. 

These toilets are bulkier than their dry flush cousins, although they take up roughly the same floor space. 

Vermifilter toilets

A vermifilter toilet uses some flushing water and earthworms to aid with the decomposition of the compost. The solids (poop and toilet paper) are broken down by bacteria and the earthworms to produce a humus with a significantly reduced volume. 

Some users of dry toilets also add earthworms to their mix to help with the decomposition process.

Dry Flush (waterless) Toilets

Otherwise known as ‘slow composting’ or ‘moldering’ toilets, these are the most popular category of composting toilets, and the one that we’ll be focusing on in this article. Here, the initial part of the composting process takes place in the toilet’s in-built chamber. The chamber is then emptied regularly into a larger compost pile away from your residence. The main benefit of this is that the toilet unit can be smaller.

The most popular brands, Natures Head and Air Head, both separate the urine from the solid waste. This helps to prevent the foul odors that occur when urine and poop collide. You’ll actually be surprised how little odor there is. 

Composting toilets don’t stink!

For the rest of this article we’ll be concentrating on the dry flush variety of composting toilets. 

What processes are in action?

When thinking about how does a composting toilet work, its important to understand the processes in action. The main biological process of composition is a fairly simple one, but one that can be improved or hampered by external factors such as temperature, drainage, aeration and ventilation.


The best carbon to nitrogen ratio for composition is around 30:1. Urine has a high nitrogen content, but as dry toilets divert the urine you don’t need to worry about this. Instead, just add some sphagnum peat moss or coconut fiber to maintain the right consistency and you should be fine. 


Heat will speed up the composting process in your dry toilet and kill pathogens that may be in the waste.  Decomposition will naturally generate heat, but if the chamber of your dry toilet is too small to get hot enough for quick decomposition or liquid evaporation, a heater may be used.


Aerobic decomposition is faster and less smelly than  anaerobic decay [1]; therefore, we should maintain a certain amount of air throughout the pile to maintain aerobic conditions. Thankfully, this is easily achieved by turning the crank handle on the side of your toilet. 

The end result

Properly composted human waste does not contain any pathogens or viruses, as these are destroyed during the bacterial breakdown. You are then left with a nutrient-rich fertilizer which can be used in the garden, reducing your need for commercial fertilizers and preserving local water quality. Do note that human waste should not be used to fertilize any edible products. 

In 2006 the WHO set up guidelines on how human waste can be reused safely by following a ‘multiple barrier approach’ [2].

Throw the compost on it!

The components of a composting (dry) toilet

Another crucial step to understanding how does a composting toilet work, is learning about the components in the toilet itself.

Urine diverter

This is the crucial part of the system that separates the pee from the poop, and avoids all those awful smells. The design is simple but effective; you’ll get used to using it really quickly, but will have to explain how to use it whenever you have guests! 

Composting chamber

All the poop is collected in the composting chamber. The Nature’s Head is rated for 90 uses, or about 3-4 months of regular use per adult. Simply empty it out when the level gets to about the crank handle. Don’t use bleach or other chemicals to clean it as they mess with the decomposition process. 

Crank handle

This sits on the side of the composting chamber. Give it a turn after every use to keep some aeration in the mix.

Best Overall
  • 12-volt shroud fan
  • Spider and shifter handle
  • Power hook-up
  • Urine bottle with a capacity-indicator window


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Best Value
Air Head Composting Toilet
Air Head Composting Toilet
  • Urine bottle with a capacity-indicator window
  • Ventilated Solids hatch
  • Removable 
  • Seals and lids 
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Want to lean more about how does a composting toilet work? Check out the resources below.

[1] Compendium of Sanitation Systems and Technologies – (2nd Revised Edition)       

[2] WHO Guidelines for the Safe Use of Wastewater, Excreta and Greywater (Volume IV: Excreta and greywater use in agriculture)

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