PVC backwater valves prevent sewage backup in drainage systems by blocking backflow with a flapper that is forced into a closed position if sewage starts accumulating. Their stepped construction encourages water flow, and the flapper and cover have an elastomeric gasket to ensure a watertight seal. With a magnetic strip for underground detection and threaded access cover for easy inspection, maintenance is simple. With the extension kit, installers can safely bury the valve as required by code in many states. The kit includes a 16 in. sleeve, a plastic lid, and an adapter.