- 1). Lift the lid off of the tank.
- 2). Identify the type of ballcock the toilet is equipped with. A traditional plunger-valve ballcock features a plastic or metal ball attached to a threaded float arm. A float cup ballcock features a rubber canister that rises and lowers along a vertical tube. A floatless ballcock is mounted within the bottom of the interior tank and features a rubber hose attached to it.
- 3). Adjust a traditional plunger-valve ballcock by bending the float arm downward slightly. Note that a float cup ballcock features a thin metal wire along its side that attaches the float cup to the top of the vertical tube. The wire is attached to the float cup with a spring clip. Pinch the two ends of the spring clip together, push the float cup down slightly, then release the clip. Lower the water level on a floatless ballcock by turning the screw at the top of the hinged end of the ballcock in a counterclockwise direction one-half turn with a screwdriver.
- 4). Flush the toilet and note the water level within the tank at its highest point. Continue adjusting the ballcock to lower the water level if water still trickles down the overflow pipe.
Source...