Abstract: A water saving device for a toilet tank comprising an open top container with partitions forming an inverted U, siphon duct opening adjacent the bottom of the container and extending over an end wall to discharge below the container bottom. A top wall seals across the tops of the partitions, with a check valve therein to prevent the entrapment of air. A vent tube opens through the top wall from outside the toilet tank and a shut off valve is selectively operated to open or seal off the vent tube.