Universal replacement toilet tank

A universal replacement toilet tank (10) that incorporates within a toilet tank (12) a piston flush valve (40) that functions in combination with a ballcock (22), a water closet (30) and a pressure increasing riser (120). The valve (40) is designed to be easily adjusted to allow a selected volume of flush water to flow from the toilet tank (12) into the water closet (30). The pressure increasing riser (120) consists of a hollow pipe (122) and a decorative sleeve (140) that are positioned between the toilet tank (12) and the water closet (30). The riser allows the toilet tank (12) to be elevated above the water closet (30) to provide an increase in the pressure of the water that is used to flush the water closet (30). The invention also includes a threaded adapter (100) having upward internal threads (102) and downward external threads (104). The internal threads (102) are threaded into the threaded section (96) on the flush valve attachment structure (84) and the external threads (104) are inserted through a water egress port (24) on the toilet tank (12). The adapter allows the universal replacement toilet tank (10) to be used with various designs of water closets (30).