A pop-up water relief valve (also commonly known as a pop-up drainage emitter) that is normally closed except when there is a build up of hydrostatic pressure. As the drainage pipes fill and build up slight pressure, the cover rises to allow the excess water to escape. Once the water is discharged the pressure drops and a stainless steel spring automatically retracts the cover to it's closed flush position. The flush design of the product ensures that it blends well into the surrounding area. It is manufactured from a structurally foamed High Density Polyethylene (HDPE) with a UV inhibitor to reduce sun damage. Typical application is at the discharge end of the drainage pipe. Can be installed in either a vertical or horizontal position. APU model fits either 3″ or 4″ Sewer and Drain hub fittings while the APU3 and APU4models fit 3″ and 4″ Sewer and Drain Pipe and Triple Wall Pipe, respectively. APUP34 fits 3″ and 4″ Triple Wall Pipe, Corrugated Pipe and Sewer and Drain Pipe.