A screen decanter for decanting liquid from a reservoir, comprising at least one rack comprising screens and baffles forming the sides of a cavity; a frame attached to the screens and baffles and providing a barrier so that liquid cannot pass from outside into the cavity without passing through the screens; a patterned perforated drain pipe inside the cavity and leading to an opening through which liquids may drain out from the cavity. The pattern of the openings counteracts the hydrostatic head within the rack such that flow through the screens is uniform at all depths of immersion in the liquid reservoir. Preferably, the screens have a porosity of about 50 micrometers.