The Sioux Chief 869-4P 4" PVC check valve backwater device is designed to prevent any unwanted backup in sewer lines. It features threaded access seals that are hand tight, and allow easy maintenance and inspection. This valve allows unrestricted flow in the downstream direction but closes and prevents the reverse flow of water back into the sewer system. Sioux Chief is one of the industry leaders in both innovation and affordability. We carry this check valve at very affordable prices. Grab it here now, here at PlumbersStock.