Abstract: A buoyancy control unit for the flapper-type ball valve of a water closet flushing unit includes a flexible air release metering tube of a smooth plastic connected to the outer peripheral portion of the flapper valve ball and extended upwardly from the stored water level. An adjustable meter valve is secured about the tube to adjustably collapse the tube for metering flow of air. A simple strap hanger has an offset apertured support tab through which the tube passes and on which the meter valve rests. The opposite strap end is bent and hooked over the edge of the tank. A stick pin is secured in the ball end of the tube and the tube is secured in a pin threader which passes through the opened bottom of the ball and the tube opening to insert the tube with the pin abutting the interior of the float ball.