Flush tank tool for replacing a ballcock assembly

A tool for facilitating the replacement of a ballcock assembly in the flush tank of a toilet and preventing the leakage of residual water, wherein the tank includes a bottom wall, upstanding side walls and two spaced apart openings in the bottom wall, a flush valve at the bottom of the tank mounted at one of said openings, a ballcock assembly mounted in the tank at the other opening and having an inlet shank extending through said other opening and being sealingly secured to the bottom wall by a shank nut and sealing members, said tool comprising an elongated tubular body of resilient material, a tubular stiffening core of rigid material within said body to prevent collapse of said body when it is in sealing engagement with the shank opening, and a plug within the core to seal against the passage of water therethrough, said core being sized to fit over the shank of the ballcock assembly after the shank nut has been removed, and said resilient body sized to sealingly engage the opening through which the shank extends to plug the opening and prevent leakage of water from the tank when the ballcock assembly is removed, whereby insertion of said resilient body of the tool to engage the opening is coordinated with the removal of the ballcock assembly from said tank and said tool is removed upon the coordinated replacement of either one of a repaired and a new ballcock assembly after which the shank nut is placed on the shank to sealingly assemble either one of the repaired and the new ballcock assembly to the flush tank.