Abstract: A toilet supply tank assembly having high performance flush characteristics is designed to maximize water pressure over the flush valve and to minimize fluid turbulence within the tank during a flush cycle. The tank includes a bottom interior surface which tapers downwardly from the outer edges thereof to an fluid escape opening, and may include a cylindrical tank having a frusto-conical bottom portion with the fluid escape opening at the most narrow portion thereof. In order to further reduce turbulence created by water flow within the tank during a flush cycle, a cylindrical flush valve plunger having a frusto-conical stopper portion is provided which has no abrupt transitions. The tank may also include at least three vertical partitions intersecting a common axis which not only provide a cage in which the flush valve plunger can slide up and down, but also prevent the water from swirling and forming an energy robbing vortex.