A cistern outlet valve assembly (10). The assembly includes an outlet orifice (14) and a buoyant member (20). The buoyant member (20) has an outlet seal (22) on one side and a housing seal (26) on the other. The assembly (10) also includes a valve housing (18) is adapted to cover the buoyant member (20). The housing (18) has large clearance guide means (30) adapted to guide movement of the buoyant member (20) from a closed position in which the outlet seal (22) seals against the outlet orifice (14) and an open position in which the housing seal (20) seals against the housing (18). When the buoyant member (20) is in the open position any fluid incident on the guide means (30) is prevented from flowing onto the buoyant member (20) by the housing seal (20) sealing against the housing (18).