How does a composting toilet work?

portfolio of composting toilets

Usage and functioning of composting toilets

Have you ever wondered what a composting toilet is and how it works? Why should you get one for your travels? In this blog post, we have summarized the most important aspects of it.

Chances are high that you looking for more information regarding composting toilets when you read these words. The good thing is: You are absolutely in the right spot! In this article, you will learn what a composting toilet is, how to use it and how it functions.

Afterwards, you will hopefully understand why we are such big fans of these products and have created our own brand, to help even more people to enjoy the benefits of portable composting toilets, i.e. spending more time in places they love! 

TL;DR: A composting toilet works as follows:

  1. You sit down
  2. A separator divides liquids and solids in two separate containers:
    This separation is the first step to prevent smells
  3. You add a carbon-rich cover material (litter) to your solids after each use:
    This cover material is the second step to prevent smells
  4. There is no flushing / water usage and no chemicals
  5. You can dispose liquids and solids separately once filled up

camper van in nature next to lake

1. The concept of a composting toilet

A composting toilet separates your urine from your solids. That is why we also refer to it as a separating toilet. And it does this in a very simple way:

With the so-called urine separator.

Why separate? Because not separating, i.e. mixing, liquids and solids, as with a normal toilet like at home or a camping / chemical toilet, creates all of the things that you want to avoid: Smell, weight (as you use water to flush), short emptying cycles and unpleasant emptying procedures. By separating, you are avoiding all of these problems and make life much more convenient.

First things first: You need to sit down when using a composting toilet, otherwise the whole system won't work. 

The composting toilet consists of only three main elements:

separating toilet mechanism
  • Urine separator (separating toilet insert)
  • Solids container or bucket, lined with a (compostable) plastic bag
  • Urine canister (This can also be replaced by a hose to transport the urine into a larger tank)

In addition, you will of course need an appropriate box and a toilet seat.

Liquids and solids are collected separately in the composting toilet. Typically, the solid matter in a bucket in the back (lined with a plastic bag) and the urine, in a canister, in the front. Those two can then also be individually be emptied. 

Trelino inside image

Sometimes, you hear the term "dry toilets". These are also waterless toilets but they lack the separation. Instead they collect both the liquids and the solids in the same bucket. That still gives you many of the issues listed above and therefore we prefer the separation method.

Important reminder: To ensure that the separation works according to plan, you must use the toilet in a seated position. Otherwise, proper separation is not guaranteed. This is because the urine separator is anatomically designed for a person sitting down. 

2. A composting toilet doesn't smell

As you learned in the first section, the separating mechanism creates a variety of advantages. One of the biggest is surely the smell. Where does the normal smell of a toilet go?

Well, it's actually pretty simple. Nature has already provided a mechanism for the separation of liquids and solids in most living things and for a good reason. 

Part A: Urine by itself is pretty harmless and doesn't really smell much. It actually contains a lot of nutrients, such as nitrogen (high levels), phosphorous and potassium. It is thus an excellent fertilizer. 

In the context of the composting toilet, it should be mentioned again here that urine only begins to decompose after a long period of storage and thus the odor formation.

The well-known urine smell is primarily caused by the combination with water, especially with the lime dissolved in it. Another factor responsible for the odor is the urine scale that builds up over time.

So the longer urine is collected, the more likely it is that odor will be perceived. For this reason, most urine-diverting toilets have a maximum of one 10-litre canister, which lasts for about 2-4 days.

trelino smart separating system

Part B: Your poo is also pretty harmless by itself. The main thing here is that you want to dry the poo as quickly as possible because once it is dried, the smell is gone. The drying of solids is the open secret behind a functioning composting toilet. 

You can achieve this in two ways:

1. Use a cover litter material, such as saw dust or small pet litter to speed up the drying process. The material should always contain some amount of carbon. All the moisture is absorbed by the litter and released through the fibers so that everything can dry off. However, if the litter is collected for a longer period of time and if you travel in hotter climates, condensation will form over time. 

This can be prevented or regulated by leaving the lid of the composting toilet open from time to time or by using a fan. This allows the moisture to evaporate.

2. A fan can be used as a support or alternative to the litter. This ventilates the moist warm air outside and allows the solids to dry. The fan also removes freshly formed odors, so that the overall odor formation is somewhat reduced. By using a fan, you can collect for longer. Without a fan, the disposal intervals are somewhat shorter. 

3. Why does a composting toilet not require water?

As previously mentioned, a composting toilet is also always a dry toilet. This means that it does not need water for flushing.

Your solids fall directly into the solids bucket due to gravity without touching the urine separator. The bucket is also used to dry and store your stool.

The urine is fed through the funnel-like design of the composting toilet insert at the front into the urine canister or with a hose into a urine tank. Here, too, you don't need water for flushing.

The big advantage here is that with a urine-diverting toilet you don't waste precious drinking water for flushing, which you have to dispose of afterwards.

4. Why does a composting toilet not require chemicals?

Since you separate your solids and urine, you don't need chemicals like a regular cassette toilet.

Why is that?

The chemicals in cassette toilets have to be used because both liquids and solids are mixed together. This creates a lot of unpleasant smells and by adding certain chemicals, this smell is neutralized. 

5. What kind of litter material should I use?

As you learned in the beginning, the solids are collected in a separate container. This is always lined with a plastic bag in which the solids are dropped. 


trelino origin s in garden setting

Before the first use, you should add two scoops of litter material, e.g. small pet litter or saw dust, to the bottom of the container. 

Then, after each use, depending on the amount of solids that you dropped, add one to three scoops of litter material to cover up your recent business. 

Regarding the material itself, we wrote a separate blog post on that topic. Have a look here and read about the different litter options for your composting toilet.

That's it, pretty easy!

6. How do you dispose waste from a composting toilet?

It's rather simple because you can empty the two independently of each other:

  • Solids (possibly with your litter, e.g. saw dust)
  • Urine canister

You can either dispose of your solids in a compost* (if you have one) or simply add them to your regular household trash (check your local regulations, since some states have specific rules). Think of it as a diaper or dog waste bag.

The urine can be poured down any public (regular) toilet or sewage system. Otherwise, it can also be diluted and used as fertilizer* in your garden. 

Summarized: By using a composting toilet, you no longer need dedicated disposal stations for your cassette toilets. Therefore you can travel for much longer trips off-the-grid and properly enjoy nature and the outdoors.

Let's face it: The composting toilet is the toilet of the future. It saves resources and is sustainable. Plus it gives you all the freedom you want for your travels!

Interested? Have a look at our collection of high-quality and comfortable composting toilets.


*please follow the regulations of your municipality and be careful if you are taking medication, this could prevent composting and also be harmful to the soil