A hopper comprises a suction conduit and a pressure conduit each connected to a pump for discharge of the hopper contents, the suction conduit being horizontal and communicating at its free end via a control valve with water outside the hopper, a plurality of vertically extending suction pipes extending downwardly from the suction conduit and spaced above the hopper bottom, each suction pipe having a valve, and cone-shaped bottom valves below the suction pipe open ends for conducting water from outside the hopper to the suction pipes.