The single most common question people ask about composting toilets is: "Will it smell?" The answer depends almost entirely on one thing — whether you're using a urine separator.
The chemistry of the smell
It might surprise you to know that urine is actually sterile and relatively odour-free when fresh. Solid waste has its own smell, but it's manageable. The problem comes when the two mix.
When urine and faeces combine, they create warm, wet conditions ideal for anaerobic bacteria. These bacteria produce ammonia and other compounds — and that's where the familiar, eye-watering smell comes from. Mix urine and solids together in a composting chamber and you'll be fighting odour forever, no matter how much sawdust or carbon material you add. Separate them, and the problem largely disappears.
What a urine separator actually does
A urine separator is a shaped piece of plastic that fits underneath your toilet seat. It catches liquid waste and channels it away through a pipe, while solid waste drops straight down into the composting chamber below.
The design is deceptively simple — no moving parts, no electricity, no complicated mechanism. Just a carefully shaped diverter that uses gravity to keep two waste streams completely separate.
The benefits go beyond smell
- Faster composting: Solid waste dries out much more quickly without urine keeping it wet. Dry material composts faster and is easier to manage.
- Less frequent emptying: With liquid removed, the volume of material in your composting chamber is dramatically reduced.
- Better compost: Separated solid waste produces cleaner, more stable compost that's easier and safer to use in the garden.
- Versatile urine disposal: Separated urine can be piped to a soakaway, a planted bed, or a separate container. Diluted with water, it's an excellent nitrogen-rich fertiliser.
Does it work for everyone?
Yes. Our We-Pee separators are designed to work for both male and female users. The shape and position of the diverter ensures liquid is caught and redirected regardless of how the user is seated. The key is correct positioning during installation — the separator should fill the front third of the toilet seat hole.
A simple change with a big impact
We've been making urine separators since 2009, and the feedback from customers consistently confirms the same thing: fitting a urine separator transforms the composting toilet experience. What was previously a high-maintenance, odour-prone system becomes simple, clean and genuinely sustainable.
If you're building or upgrading a composting toilet, urine separation isn't an optional extra — it's the foundation everything else rests on.