XH81, XH81A, XH41, XH41A rubber drain check valves (referred to as "duckbill flexible check valve" in Spain and "duckbill rubber flat valve" in the United States) are summarized, exemplary and revolutionary redesigns based on the production of Japan OSS Valve Company in Spain and Red Valve Company in the United States. It is also committed to continuously improving the rubber blowdown check valve (duckbill shaped flexible check valve), which greatly improves the strength, toughness and sealing of the valve. The valve has no moving components and is free of any maintenance. The valve can be used for straight pipes, flanged pipes, cement pipes and glass steel pipes. The valve is widely used for coastal, beach, wharf, reservoir, municipal flood discharge and sewage discharge. It can be said to be an environment-friendly green valve. The valve replaces the flap door check valve, completely solving the problem that the flap door is easily blocked by sediment, silt, rocks, vegetation and marine organisms.