Polylok PDB-4PE-KIT-IT4X4CC 4" Flow Gate with Elbow and Corrugated Pipe Adapter - The Polylok 4" Flow Gate is designed to help solve multiple drainage needs. It can be used with 4" drain and sewer fittings. Allows water to be diverted and released to water-safe areas away from structures, erosion-prone landscapes and poor drainage areas. When water enters a drain pipe, it needs to go somewhere. The flow gate attaches to either 3" or 4" hub sewer and drain fittings, and pops up when the pressure of the flowing water hits it, allowing the water to discharge. Once the water stops flowing, the flow gate closes again blocking anything from falling in. Just press the flow gate into the pipe, and forget worrying about finding debris, rodents, or anything else you don't want in your pipes.