A filtration vessel has an inlet for inflow into the filtration vessel of liquid media to be filtered, a body of filter media in the filtration vessel, and a drain to receive filtered liquid media for take off from the filtration vessel. The inlet is configured to induce rotating flow about the vessel of unfiltered liquid present in the vessel; and/or, the drain is configured in backwash mode to force backwash liquid through the filter media in rotating flow about the vessel; and/or the drain includes drain limbs inclined to the horizontal and providing for draining of filtered liquid along the inclined limbs to outlet.