Available in 1¼" and 1½" sizes BSP female inlet nut x universal compression outlet Membrane opens under water pressure to allow discharge to flow freely and then closes to form a seal to prevent foul odour or sewer gas entering the building Can be fitted in horizontal or vertical position Can be fitted in installation where a non-return valve can be of benefit to the plumbing installation No water seal so it can never dry out through evaporation or lack of use of an appliance as the membrane remains sealed Not recommended for use with shower trays unless there is access for maintenance Patent Pending