The NDS Back Water Valve is designed to protect low areas or basements from the backflow of waste from street sewers. The quick action flapper allows unrestricted uni-directional flow. An elastomeric gasket in the flapper ensures a watertight seal. The flapper can be easily removed and replaced if required. A threaded access cap is designed for hand tightening. Valve hub outlets fit 2", 3", 4" or 6" DWV pipe and may be adapted to 2", 3", 4" or 6" sewer and drain pipe with NDS DWV to sewer and drain adapters.