A toilet flush valve that has a moveable buoyant float therein, wherein the float has an open bottom end to trap air therein and wherein the housing includes controls to selectively release air to allow the float to move upwardly therein to permit flushing. By timing when one or two air vents on the housing are open, the duration and volume of the flush can be controlled, with the buoyancy provided by the water lifting the float to open the flush valve. This provides a flushing system with minimal activation energy.