Guidelines for the design of self-cleaning wet wells for variable speed pumps are given. The progress of research on the design of wet wells for constant speed pumps, including submersible pumps, is reported. A self-cleaning wet well is one from which scum, sludge, and other deposits can be ejected by the main pumps during pump-down–lowering the liquid level to the pump suction inlets for a short time. During normal operation, the wet well water level is the same as the level in the influent sewer, so there is no cascade, no air entrainment, and little turbulence.