Holding tank vacuum relief

摘要

A plastic sewage holding tank (117) in a boat, associated with a toilet, includes a vent check valve (140) for providing vacuum relief. By mounting the vent check valve in the top (118) of the tank, when the tank is being emptied by rapid pumpout implosion or other damage to the tank is prevented. The vent check valve may include a valve body (141) with an interior surface (143) mounting a quad sealing ring (75), with a valve element (153) guided for reciprocal movement between a sealing position where an axially elongated substantially cylindrical peripheral surface (146) of the valve element engages the quad ring (75), to an open position where the valve element is moved against spring bias away from the valve body. A spider (80), with a collar (81) for guiding a shaft portion (149) of the valve element (153), may mount a coil spring (159) to provide a biasing action.