A ball cock for a flush tank having a valve chamber connected with a discharge chamber. A float operated piston valve is mounted in the valve chamber to control water flow to the discharge chamber. A hush tube connected to the discharge chamber feeds the water to the bottom of the flush tank. A combined volume control and anti-siphon valve is mounted in the discharge chamber between the inlet and hush tube to regulate the rate of flow and to act as a vacuum break under conditions of negative pressure in the water supply line.