What to do when your grey water tank freezes

Which part of the system has actually frozen?

Before you try to fix anything, work out where the problem actually lies. It isn't always the whole tank that's frozen – often it's the drain pipe, the drain valve, the trap, or water left in the lowest part of the system.

If water from the shower or sink won't drain away, the problem is probably inside the vehicle. If water drains normally into the tank but you can't empty it, it's more likely the drain valve or the lower part of the system that's frozen.

Don't force it

Never try to force a frozen valve open. Plastic valves and pipes become more brittle at low temperatures, so applying force can damage the lever, the seal or the valve itself.

The same applies to pipes. Ice expands as it freezes, which already puts the system under strain. Extra mechanical force can cause a crack that you won't notice until after it has thawed.

If possible, move the motorhome somewhere warmer

The safest way to thaw the system is gradual warming. If you can, move the motorhome into a heated garage or service area – or at least somewhere sheltered from wind and severe cold.

If the tank sits in a heated double floor, simply heating the living area for longer often helps. What matters is giving the system enough time for the temperature to rise gradually – never with an open flame.

Use the drains as little as possible while thawing

If you know the grey water tank is frozen, cut back on water use temporarily. Every wash and shower sends more water into the system.

If the outlet is blocked with ice, the tank can overfill or water can start backing up through the pipes. Until the system is draining normally again, it's best to keep drain use to a minimum.

• Winterising a motorhome: how to prevent odour and mould

Once the system has thawed, empty it thoroughly

After thawing, empty the grey water tank completely. It isn't just about the risk of it freezing again: if water has sat there for a while, it will contain food residue, grease, soap and other organic matter.

Freezing and thawing doesn't remove this build-up – if anything, it stays on the tank walls and inside the pipes. That's why the moment after thawing is the right time for a thorough clean of the grey water system, for example with Iza Effect Fresh Tank.

• Fresh Tank – cleaning the grey water system

Fresh Tank

Purpose-built cleaner and odour neutraliser for grey water tanks, drains and toilet cassettes in motorhomes, caravans, campervans and boats.

Read more

Add to basket

Fresh Tank is not a substitute for an empty tank

Emptying removes the liquid, but not the build-up that accumulates over time. That's why even a regularly emptied tank can eventually start to smell.

Occasional cleaning with a dedicated product is worthwhile especially after extended use, when odours appear, after long periods of storage, and after problems with frozen water. After cleaning, rinse the system thoroughly and check that water drains normally through all outlets.

• How to clean the grey water tank and prevent odours

What to check before you set off again

Once the system is working again, take a few minutes to inspect it. Cracks often only become apparent once water is flowing through the system again.

• Does the drain valve seal properly and open smoothly?
• Are there any visible cracks or drips on the pipes?
• Does water drain from all outlets as quickly as it did before?
• Has the tank been rinsed thoroughly after cleaning?