How to prevent foul water backing up from the drainage system?
For a residential property in the UK, a 4 inch / 110mm drain non return valve will prevent foul water backing up the drain pipe from the sewage system. For commercial property, 6 inch / 150mm drain non return valve is required. The drain pipe will be found in the main drains inside an inspection chamber located outside your property. With the Buffalo Non Return Valve, the valve will fit in PVC or clay pipes. You may also want to consider a non return valve for sinks and baths, which have a 40mm waste pipe.