What Do I Do With Waste from a Composting or Dry Toilet?

Learn how to safely process and reuse waste from dry and composting toilets, turning it into eco-friendly compost or garden fertiliser.

Composting and dry toilets are an increasingly popular choice across the UK for those looking to reduce water use, live off-grid, or make their homes and holiday sites more environmentally friendly. These waterless systems are easy to use, require minimal maintenance, and are designed with sustainability in mind. However, one of the most common questions new users ask is: What do I actually do with the waste?

In this blog, we’ll walk you through how to handle, process, and reuse waste from both composting toilets and dry toilets, using guidance from Biolan’s tried-and-tested models: the Simplett, Simplett Plus, and Composting Toilet

First, Let’s Understand the Types of Toilets

Dry Toilets like the Biolan Simplett and Simplett Plus do not contain any internal composting mechanism. Instead, they collect solids and liquids separately, and the solid waste is transferred to an external composter such as the Biolan Quick Composter 220eco to fully complete the composting process.

Whilst many dry toilets listed online claim to be “composting toilets” - they really aren’t. They are simply waste separators and collectors. Proper composting needs time, heat and bulk to convert a waste product into usable compost - and dry toilets do not provide these conditions. They are the first step in the process - read on for more details.

Composting Toilets such as the Biolan Composting Toilet are thermally insulated units that composting inside the toilet itself, turning waste into humus (a soil-like substance) over time. These are designed to be emptied less frequently and work well in year-round use.

What Happens to Solid Waste?

1. In Dry Toilets (Simplett & Simplett Plus)

Solid waste is collected in a removable container - usually 28-30 litres in capacity. You can use a biodegradable liner bag in the container to make emptying cleaner and simpler or pad out the container with newspaper at the bottom. When full, the bag and contents are transferred to an external composter for further processing, which will take some time.

It’s important not to compost the contents directly into the ground or in your garden without proper treatment. Human waste needs time to break down safely to eliminate pathogens. In a compost bin:

Add a bulking material to maintain the right balance for aerobic decomposition and reduce odours.
Turn the contents regularly and keep the pile moist (but not too wet) to encourage breakdown.

Leave the compost for at least one year before using it. When fully matured, it should be dark, crumbly, and odour-free- very similar to soil.

It’s advisable to use composted human waste around trees, shrubs, or ornamental plants only, rather than directly on fruit or vegetable beds, unless local guidance permits.

2. In the Composting Toilet eco

This toilet model is designed to composting inside the unit. Thanks to its insulated structure, the composting process can continue year-round - even during cold UK and Irish winters.

Use a spade to scoop out the matured compost from the hatch at the unit’s.
Use the compost as top soil or compost for a 6 months in a different container for use as a mature compost material.

It’s recommended to only remove the content up to the top of the service hatch, to ensure the composting process remains active.

What About Liquid Waste?

Both dry and composting toilets separate liquid waste (mainly urine) from solids but in different ways. Managing this part of the waste “stream” is just as important.

How to Handle Urine / Seep Liquid

In the Simplett and Simplett Plus, urine is collected in a separate canister (usually outside of the toilet cabin / hut. Canisters are typically 10 litres in volume and should be emptied every few days depending on use. Remember, if we all drink about 2 litres of liquid per day then this is roughly the amount of liquid that will come out as urine.
In the Composting Toilet urine passing through the composter will generally evaporate, but any excess “seep” liquid will collect at the bottom of the composter underneath a specially designed seepage plate and will then transfer to a separate canister, which also needs to be monitored and emptied periodically.

Options for Disposal or Reuse:

Reuse in the Garden:
Urine is rich in nitrogen and can be a fantastic fertiliser when diluted 1:10 with water (one part urine to ten parts water). Apply it around ornamental plants, shrubs, or trees - not edible crops unless it has been stored safely for several months.
Soakaway System: In off-grid setups, a soakaway or reed bed system can be used for urine disposal. Always follow local environmental guidance.
Mains Disposal: Where possible, the liquid can be poured into a standard toilet or greywater outlet.

It’s advisable to emptying the liquid containers before freezing weather arrives, as the build-up of frozen liquid can damage the pipe or liquid collection container.

How to Stay Hygienic

Handling waste from a composting or dry toilet is surprisingly clean when done correctly. Here are some basic hygiene tips to follow:

Always wear gloves when emptying containers.
Wash your hands thoroughly with soap afterwards.
Use biodegradable liners in dry toilets to make the process easier and reduce the need for frequent cleaning.
Clean toilet surfaces regularly with natural or mild detergents - please avoid harsh chemicals: tempting as they are, they will disrupt the natural composting process as they kill both good and bad “bugs.”
Keep the toilet well-ventilated to minimise odours and support the composting process.

When Is the Waste Ready to Use?

Solid waste needs time to mature. For compost from dry toilets, wait at least 12 months before using it.
Liquid waste (urine) can be used sooner, especially if diluted. However, if unsure, store it for at least 3 months before applying to soil.

Remember: when using any compost made from human waste, always err on the side of caution and avoid using it near edible plants unless fully composted and legally permitted.

Disposing of waste from a composting or dry toilet isn’t difficult - it just requires a little planning and respect for the process. Whether you’re using the Biolan Simplett, Simplett Plus or Composting Toilet eco, the key is knowing how to handle both the solids and liquids safely and sustainably.

Once you get into a routine, you’ll find that managing waste this way is not only hygienic and manageable, but also fulfilling- turning waste into something useful for your garden while reducing your environmental impact.