How Much Toilet Chemical Do You Put in a Caravan Cassette?

Quick answer: Use the dose printed on the bottle typically measured with the cap or doseing chamber and poured into the emptied waste tank via the cassette outlet spout, then topped up with around 2–3 litres of clean water so waste stays covered. Never pour fluid straight into the toilet bowl, and never guess the amount too little won't control odour, too much is wasteful.

How do I add 40Shot to the cassette, step by step?

Empty the cassette at a Chemical Disposal Point and give it a quick rinse.
Measure the dose using the built in dosing chamber bottle's cap. 40Shot dose: is 25ml
Pour it down the cassette outlet spout , not into the toilet bowl. Pouring neat fluid through the bowl can damage the seal and blade. Add fluid via the cassette outlet spout rather than directly into the bowl to avoid damage.
Add 2–3 litres of clean water to the tank. This activates the fluid and keeps solids submerged. The standard advice is to add the measured fluid, then top up with water so waste is always covered.
Slide the cassette back in and you're ready to go.

Why does the water matter so much?

Because dry waste is smelly waste. A cassette that's left to dry out lets methane and odour build up fast keeping the contents wet is what allows the fluid to break everything down. Keeping waste and paper wet inside the cassette counteracts the rapid build-up of smelly gas and helps everything break down. The few litres of water you add with the dose is doing real work, not just rinsing.

How often do I top it up?

Situation	Typical re-dose
Normal use (2 people)	Every empty — re-dose each time you empty and rinse
Hot weather / heavy use	Empty and re-dose more often (every 2–3 days)
Cassette getting smelly before it's full	Empty early — don't wait for it to fill

As a rule of thumb, a cassette is best emptied every 3–5 days at most, which is roughly all one will hold anyway. Good practice is to empty the cassette every 3–5 days at most. You re-dose every time you empty.

Common dosing mistakes

Pouring into the bowl, not the spout — risks the seal and blade.
Skipping the water — the single biggest cause of avoidable smells.
Under-dosing to save money — you lose odour control and just empty more often.
Using pink in the cassette — pink is a flush-tank additive (see Post 1).

Key takeaways

Dose by the bottle's measure, not by eye.
Add via the outlet spout, then top up with water.
Re-dose every empty; empty every 3–5 days.
Keeping waste wet is what stops the smell.

40Shot 2-in-1 fluids break down waste and control odour in a single dose — formaldehyde-free, made in Britain by Qualkem.

FAQ

How much 40Shot do I use per fill? One 25ml doosel then top up with 2–3 litres of water.

Can I put toilet chemical straight in the bowl? No. Always add it through the cassette outlet spout. Neat fluid in the bowl can damage the flush mechanism and seal.

Do I need to add water as well as chemical? Yes. Add 2–3 litres of clean water with the dose so waste stays covered and the fluid can work.

How often should I empty and re-dose? Empty every 3–5 days at most (sooner in hot weather), and add a fresh dose each time you empty.