In a wastewater treatment plant a clarifier is fitted with piping and a pump to withdraw settled sludge from the bottom of the tank upwardly through the tank's center column and radially out from the clarifier via an exit pipe above the liquid level. The exit pipe can be supported on a fixed walkway. At the bottom end of the central tower is a manifold device for collecting settled sludge, including an annular preferably cylindrical wall, a central pipe hub and at least one pipe branch extending from an opening in the cylindrical wall radially inwardly to the central hub. Sludge is drawn up through a vertical sludge return pipe by a pump located preferably above the tank's liquid level, drawing sludge into pipe branches of the manifold device and through the hub to the sludge return pipe, then out through the exit pipe.