A circular tank having a generally flat bottom with a sediment well positioned at one side thereof. Feces and other sediment are brought into the well by inducing a circular movement to the water within the tank to move the sediment around the tank and into the well. The tank preferably includes a standpipe arrangement within the well which continually removes the sediment from the well. The tank is preferably situated with the bottom sloping toward the sediment well. In large tanks, jets of water are positioned adjacent the bottom to jet the sediment up the slope of the tank where the circulation of the water then moves the sediment downwardly to the sediment well. Charged air bubbles are used to produce a froath of the dissolved protein surrounding the standpipe so that waste water also removes the protein. The tank is preferably made out of fiberglass so that it has very smooth internal surfaces which do not retain the sediment. The tank is inexpensively constructed using a fiberglass coated plywood bottom that is supported on a polygonal frame located centrally of the tank with the sediment well positioned between the frame and the sidewall of the tank. Outriggers from the frame extend under the sidewalls of the tank on opposite sides of the sediment well so that the sidewalls are utilized to carry verticle load and decrease the stresses in the bottom of the tank.