Sewer Relief Plug (Pop Off Cap) 3-in and 4-in White Round CleanoutSewer Popper Cleanout and Relief Valve pops up automatically whenever theres backup in a sewage system releasing sewage overflow outside, rather than inside the home. A quick, cost effective way to prevent a nasty and expensive problem, this product can save thousands in property damages. Additionally, with the Sewer Popper you can service the fill line instead of the tank itself providing further savings and peace of mind. Automatic pop up releases