A liquid filtering apparatus is placed in a vessel having a bed of filtration material and an intake for introducing unfiltered liquid, that includes a washbox, an airlifting tube extending from the washbox and including an intake end and means for introducing a primary gas to the airlifting tube, the airlifting tube passing through a central pipe, which extends from just below the washbox to a position just above the intake end. At least one screen cartridge is oriented in a generally angular downward direction in the bed and is in communication with an effluent chamber defined in part by the outer surface of the central pipe. A reject line extends from the washbox, and an effluent collector extends from the effluent chamber. A method of filtering and cleaning the filtration material is also disclosed.