Backflow Preventers can be used in drainage systems where necessary. This product should be installed in horizontal drainage lines to reduce or prevent sewage backup damage to the residence. Backflow Preventers have an innovative stepped design, in order to encourage flow and provide adequate fall through the valve body. The Flapper is installed into the valve body via a removable carrier, which utilizes a key-to-slot mechanism to ensure proper alignment. The Flapper has a permanent, one-piece sealing surface, thus allowing for unrestricted, unidirectional flow. The valve body is sealed by an impact/solvent resistant lid with an o-ring. It can also be adaptable to either shallow or deep-buried installations.