A basement floor is below the elevation of the next upstream manhole on the public sewer. What device is required to protect the fixtures on that floor?

Giải thích

Fixtures on a floor below the next upstream manhole cover elevation must discharge through an accessible backwater valve so that a surcharged sewer cannot flood the low fixtures. An air admittance valve and a relief vent handle air pressure, not backflow, and a trap primer only keeps a trap seal from evaporating.