A waste extraction system (10) for an aquaculture tank (12) includes a first conduit (18) having a first end (20) and a distant second end, with a second conduit (22) disposed within the conduit (18). The second conduit (22) has a first end (24) which is co-terminus with the end (20) of the first conduit (18). A plate (26) extends transversely across the ends (20, 24) and laterally of the first conduit (18). An axial hole (28) is formed in the plate (26) to provide fluid communication with the second conduit (22), but the plate (26) otherwise closes off or seals the end (20) of the first conduit (18). Legs (30) are formed on an underside of the plate (26) to space the plate (26) from a bottom wall (16) of the tank (12). Apertures (34) are formed in the conduit (18) near its first end (20) to allow water to flow into a flow chamber (36) created between an inner surface of the conduit (18) and an outer surface of the conduit (22). The conduits (18, 20) exit the tank (12) at a location (38) which is at least partially below the water level (40) of the tank (12). A circular flow of water is generated in the tank (12) by having a water inlet manifold directing that allows incoming water to flow tangentially to an inside surface of a side wall (14) of the tank (12). By continually pumping water into the tank (12) while maintaining the water level (40), water is drawn from above the plate (26) through the apertures (34) in the first conduit (18) into the flow chamber (36) thereby creating a general upflow of water. Solid particulate material collects by action of centripetal force into a region beneath the plate (26) where it is entrained in water and flows up through the axial hole (28) in the plate (26) into the second conduit (22) and out of the tank (12).