Backflow in a bathroom can be prevented by installing a non return valve to stop backwater coming up the foul pipe.

What is backflow in bathroom?

Backflow is sewage coming up the foul pipe from the drainage system. One of the major causes of damage as a result of flooding is backflow from sewage system. In a flood event, their is a risk of the sewers backing up and can lead to excrement entering your property from the toilet. Another cause of backflow is blocked drans further away from your property, leading to a build up in the drainage system. Over time, this build up increases pressure in the drains and foul water cannot leave your property.

How do you prevent backflow?

Backflow creats an an unpleasant experience, but it can be easily prevented. There are a number of ways to prevent this from happening:

  1. Install a Non Return Valve (backflow prevention device)

The main cause of backflow arises in the drainage system, therefore you will need to install a drain non return valve. Outside your property, you will find an inspection chamber. It is likely to be located in the road or pavement, but in can be located in a number of places. The chamber will have multiple soil pipes entering into it, which will be the waste pipes from you and your neighbours. Within the inspection, on the inlet pipe, you should install a non return valve. This can be done in minutes, with our simple push fit non return valve. The benefit of the non return valve is it provides passive flood protection, so even if you are not in your property you are protected against backflow. The Buffalo Non Return Valve also prevents rats and vermin from entering the property, as well as noxious fumes.

What type of valve prevents backflow?

The standard foul pipe diameter for homes in the UK is 110mm drain non return valve, and commercial properties the standard is 150mm. We have a 150mm non return valve also, click here for more information.  

You may also require a non return valve for the waste pipe in the sink. This is usually 35mm.

2. Toilet Bung

A reactive flood protection measure to prevent backflow would be to have a toilet bung ready to install in a flood event. The toilet bungs are easy to install, but they require you to be present to install them.

3. Remove downstairs bathrooms 

A final way to prevent backflow is to move you bathrooms above the expected flood level. By removing ground floor bathrooms, it reduces the risk of backflow because the water pressure would need to be great to push up above ground level.

How does a backflow prevent device work?

A backflow prevention device will have a single flap which will be in the closed position in normal circumstances. This prevents water coming back up the drain pipe. But if water wants to leave the property, the pressure will automatically open the valve. This acts as a one way valve, letting foul water out of the property but not back up. The valve should require a low amount of pressure (e.g. the flush of a toilet) to open and let water out of the property.

If you require any more information on backflow prevention, then call us on 0800 999 5355 or email


We offer a ranage of non return valves, available in our shop store.