Do Dry and Composting Toilets Smell? Nope! Here’s Why.

Before we dive in, let’s clear something up - when we mention “composting toilet” in this blog, we’re not talking about the old-school kind, we’re talking about modern, fine-tuned products sourced from a partner company that’s been at the forefront of reducing mankind’s environmental impact by supplying composting toilets and composting units - for over 50 years.  

So, we’re talking about a modern range of products from
[1] dry, separating toilets to
[2] advanced composting toilets.

(1)  Dry Toilets are a two-step process!

Dry, separating toilets, like the Simplett and Simplett Plus, cleverly divert solids and liquids right in the bowl. That little design tweak makes a huge difference when it comes to keeping things fresh and odour-free. Urine is diverted away to a separate container for use as a garden fertiliser, for example, and the solid material is captured inside the main container, covered by a suitable toilet bulking material, and no, not sawdust!

Once the main container is full, its contents will be taken away and emptied into a proper composting unit like the:

Quick Composter 220 eco (for 2 -5 people) or the

Quick composter 500 (for 6 – 20 people)

to complete the composting process over some weeks and months.


(2) All in one composting toilet

Composting toilets such as the Biolan Eco work in a slightly different way in that “everything” goes into the main 200 litre toilet chamber. Its patented ventilation system ensures the composting is efficient and the toilet space remains odourless.

The eco Composting Toilet unit has advanced thermal insulation, is additionally ventilated by an inbuilt air valve, an internal air channel and a tall ventilation pipe. When you first start using this toilet, the liquid separator at the bottom of the compost tank separates any excess liquid and collects it in a separate canister. Once the toilet is in use and the level of waste and bulking material has built up, the majority of any liquid evaporates during composting.

Because no chemicals or additives are required, the Composting Toilet Biolan eco benefits from a low operating cost. The bark-based Biolan Compost and Toilet Bulking Material is suitable for bedding and helps to keep the compost aerated and sustain the microorganisms that decompose materials.

Composting toilets tend to get a bad rap. The moment you mention them, you can almost see the look of mild horror on people’s faces - because they assume it must reek like a neglected festival toilet in the middle of a heatwave.

So here’s the truth: composting toilets don’t smell. In fact, if you’ve ever been around one that’s properly maintained and uses the right bulking material after each visit, you’d be shocked at how neutral the smell is. Some even have a fresh, earthy scent (like a forest floor after rain - seriously).

So, what’s the secret? Let’s break it down.

The Magic of Aerobic composting

The key to keeping things odour free is good air ventilation.

Regular toilets and septic tanks rely on anaerobic bacteria (the kind that break down waste without oxygen), and these produce gases like hydrogen sulphide (that rotten egg smell).

Composters and composting toilets  on the other hand, use aerobic bacteria, which need oxygen to do their job. Instead of producing foul odours, they break down waste into organic matter without the nasty byproducts.

Think of it like this:

• Anaerobic breakdown  =  smelly bin on a hot day.
• Aerobic breakdown = fresh garden compost.

Which one would you rather be around? Exactly.

The science behind it all.

In your separating dry toilet.

Liquids are drained off into a separate container, which can be diluted with water and added to plants without issue. (A good ratio is 1 part liquid to 10 parts water.)

Solids are collected in a removable bottom container (using a compostable bag is a good idea with newspaper in the bottom) Bulking material is added after every ‘solid’ addition. To add essential conditions for the micro-organisms (see below.)

When full, the collection container in the separating toilet is emptied into an insulated composter (with a sealed lid to ensure pests can’t get in) to continue the breakdown process. If you have a composting toilet the same process below will also take place.

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