This is a backwater valve. It keeps the cities sewer from backing into your house. It has a flapper
This is a backwater valve. It keeps the cities sewer from backing into your house. It has a flapper at the bottom of the tee that is supposed to open when when fluids or solids pass by. It can be unbolted and lifted out. to service. Sometime though it is a good place to clog up. https://plumber-oklahomacity-ok-plumbers-plumbing.com/plumbing-and-your-drain-pipes/ -- source link