Abstract: A watertight manhole insert is provided for preventing rainwater from entering a sanitary sewer system through manhole covers. The insert includes a shallow, dish-shaped body and a mounting flange designed to rest upon the supporting flange of a manhole frame. A recess is formed in the bottom of the body portion and includes a valve for releasing pressure which builds up beneath said insert. The valve is shielded such that it will not be struck by a manhole cover sliding across said insert. Additionally, the valve can be used as a handle to remove the insert from a manhole.