Does a composting toilet really not smell?

Couple sitting on Trelino toilet and van in sunset
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As outdoor enthusiasts, we've all had to grapple with the question: Where do we do our business? Do we keep a toilet on board? It's a legitimate concern, especially if you're planning on spending a lot of time using your vehicle in the great outdoors.

Contrary to popular belief, toilets don't have to be smelly. Composting toilets, or dry separating toilets, are a great alternative to the regular cassette toilet or a public bathroom. When used and maintained properly, they can be virtually odor-free. So, do they really not smell?

NO, a composting toilet does not smell and it certainly does not stink.
The composting toilet has been used and appreciated for over 90 years, mostly in outhouses. Certainly not without reason and nowadays every camper can enjoy freedom on the road with an easy-to-use composting toilet.

Separating pee and poo

Most regular toilets and all cassette camping toilets smell because they mix liquids and solids together. This problem is normally fixed by flushing quickly (at home) or by adding chemicals (for cassette toilets). If you use a composting toilet, you can do neither of those two things but there is something even better.

The first reason for the lack of unpleasant odors in composting toilets is the use of a urine separator. This device separates urine from feces, allowing the urine to be stored in a canister. This prevents the development of odors.

urine separator
The urine separator smartly divides liquids and solids into two parts

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 odour is the urine scale that builds up over time. 

So the longer urine is collected, the more likely it is that odour will be perceived. For this reason, most separating or composting toilets have a maximum of one 5.2 gallons canister, which lasts for about 2-4 days. Nonetheless, it's important to periodically clean the urine canister to prevent the buildup of urine scale.

Fresh feces naturally have an unpleasant smell due to the chemical compounds they contain, such as hydrogen sulphide, which is produced by putrefactive bacteria. However, these odors dissipate over time, just as they do in a traditional toilet. The key to eliminating odors in a composting toilet is to dry the solids, which is the second reason for the lack of odors.

Drying the poo

The drying of the solids is the open secret behind a composting toilet. Drying the solids can be achieved through the use of a litter material, such as wooden cat litter pellets or small pet bedding or sawdust, or through the use of a fan. Both options help to remove moisture, which is what causes feces to smell. As long as the feces are moist, they will produce odors. By removing the moisture, the feces decompose more slowly and through different biological processes, resulting in a lack of unpleasant odors.

Important: Each time, that you poo, you should add a handful or two or the litter material to the solids bucket. That way, to poo dries out the quickest.

wood chips composting litter material
Small pet bedding or sawdust is the best litter material


There are now many types of composting toilets with different techniques.  Does it work with litter only, i.e. without a fan or an agitator?

Yes, because all the moisture is absorbed by the litter material and released through the fibres so that everything can dry quickly. However, if the litter is collected over a longer period of time, condensation will form.

This can be prevented by opening the lid of the composting toilet from time to time, by emptying the solids bucket more regularly or by using a fan. This allows the moisture to evaporate to the outside.

Some composting toilets are designed in such a way that the solids are dried with an agitator. In these cases, litter materials are not used after each use. The agitator mixes the solids and the initial litter at the bottom after each use. This allows for longer collection intervals but also means that you need a larger and heavier toilet. Furthermore these toilets have a lot of edges and holes and can be quite difficult to clean.

Emptying pee and poo

Emptying a composting toilet also does not produce any unpleasant odors. The collected, dried solids no longer smell like feces or excrement. Disposal is simple and straightforward, whether using a composting toilet with or without an agitator, although slightly easier without an agitator. If you have an agitator, there is no compostable plastic bag lined in the solids container, which means, you need to empty the contents into a bag first.

In either case, the solids in the compostable bag are either placed on a real compost or disposed of in the nearest waste bin.


Ditch the stinky chemical cassette toilet and upgrade to a composting toilet. Not only are they better for the environment, but they also don't smell bad. As long as you keep moisture in check, you'll love your composting toilet. See our favorite composting toilets here.

We've gone in-depth on how odors are formed in a composting toilet, so now you know the science behind it. No need to worry about any funky smells - just enjoy the benefits of your composting toilet.

couple having breakfast while sitting on a Trelino
Having breakfast while sitting on your Trelino® toilet is not a problem


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1 comment

  • Jaqueline biggs

    I lived on a narrowboat(canal boat) in the UK for eight years. We replaced the cassette loo with an Airhead toilet and it worked brilliantly. It did have a fan but we eventually realized we didn’t need the mixing bar so we removed it and plugged the hole with plumbing mastic. This allowed us to use bags which was great. To cleanthe urine container we used denture tablets. Toss one in the empty container. Fill with water and let sit at least 6 hours and presto all the scale is gone and the bottle is clean. I like the design of your loos and will be buying one for my van conversion next year.

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