Abstract: An overflow valve system (10) comprises a tubular housing (12) having a J-shaped pipe fitting (14) mounted therein having an injection nozzle (24) at a first pipe-fitting end (26) located in a housing bore (40) of the tubular housing near the bottom thereof for injecting liquid axially upwardly in the housing bore and having a second pipe fitting-end (30) located outside of the tubulary-shaped housing (12). The injection nozzle has female threads therein for meshing with male threads of a toilet-flush ballcock (18), said threads meeting national standards for threads on ballcock shanks and nuts for water-closet bowls, tanks and urinals whereby a standard water-closet ballcock can be sealingly mounted in the overflow valve system by screwing it into the nozzle for controlling the flow of water through the pipe fitting into the bore.