These units are designed to easily connect a pump that is in a skimmer or vault to a flexible or rigid PVC waterline. The check valve is important for stopping a backflow of water in the event of a power loss. Each unit has a heavy duty PVC Check Valve with a MNPT fitting that screws into the pump on one end, and a rubber coupling to connect to the water line on the other end. The table below shows which Check Valve Assemblies are compatible with which pumps and skimmers.