Rainbird Drainage Pop-up Valve with PVC Elbow, 4" 4" S & D Pipe (ASTM D2729 & D3034) - 4" Triple Wall Pipe A pop-up water relief valve that is normally closed except when there is a build up of hydrostatic pressure Manufactured from a structurally foamed High Density Polyethylene (HDPE) Can be installed in either a vertical or horizontal position