a sludge collector for removing sludge from the bottom of a tank for clarifying wastewater includes an elongate curved housing placed on the bottom of the tank , with the focus of the curve being the center of the floor , the housing defining an interior cavity , and a plurality of relatively small inlets spaced along the length of the housing for the introduction of sludge from the sludge blanket . the inlets are disposed adjacent the floor to remove the most concentrated sludge therefrom . the cross - sectional area of the housing increases from the ends to the midpoint , where an outlet pipe removes the sludge from the cavity under positive hydraulic pressure and applied negative pressure . the sludge collector is designed for most efficient use with spiral or curved scraper blades in a cylindrical clarifying tank .