[vangoes]

If the "black gizmo" is connected with two hoses, that is the backflow preventer for the tank flush system. These valves are notorious for leaking and many have just simply removed them; others have replaced them with brass check valves. If the "black gizmo" is part of the drain piping system it is the air admittance valve. I removed mine and plugged it due to it releasing sewer odor.