Abstract: A method and apparatus is provided for holding first material along with less dense material in substantially separate layers and for effecting removal of at least some of the second material to a location displaced from the layer. The materials are arranged in the two layers with the first material at the bottom of a vessel and with the second material disposed above the first material. An elongate withdrawal conduit projects into the vessel to define (1) an exit port at the wall of the vessel, (2) a confined flow passageway communicating with the exit port within the vessel, and (3) at least one withdrawal aperture with the uppermost portion of any withdrawal aperture being lower than the uppermost portion of the exit port. The upper surface of the first material layer is maintained below the conduit while flow of the second material from the second material layer is effected into and through the conduit via the withdrawal aperture.