Backwater valves (sewage check valves) effectively protect rooms located on the lowest floors against flooding caused by the back flow of rainwater or sanitary sewage. A backwater valve should be installed in every home that is connected to the sewage system. This is especially true for those buildings where sanitary facilities and floor drains are installed below ground level. In addition, the sewage check valves prevent the penetration of unpleasant odors into the interior of the building due to the fact that the system is not used for a long period.