Abstract: A horizontal diaphragm with a central recess has a downwardly extending peripheral lip engaging the periphery of an open neck of a container of fluid. A vertical hollow tubular element in the neck has an upper section disposed below the diaphragm and engaging the neck periphery. The section wall defines an inverted truncated cone with spaced longitudinally extending slots. A lower section has an upper opening coincident with the lower cone end and a lower opening extending into the container below the liquid level. A vertical bore in the element has a first constriction which passes liquid disposed in the lower section. The bore wall contains a vertical cylindrical recess communicating at its top end with the cone interior. A vertical tube extends through a central hole in the diaphragm. The tube is slidable in said recess and has a second constriction interiorly disposed intermediate its ends. The tube interior is connected by conduits to the concave recess.