Overflow occurs in a toilet tank when the water supply continues to flow into the toilet bowl without stopping. The water rises in the tank after flushing and continues until it reaches the top of the overflow pipe where it flows through the pipe into the bowl. The float device responsible for turning the water supply off at the correct level is failing to operate properly and must be adjusted or replaced to correct the problem. This can be done with the proper tools and basic plumbing knowledge.
Turn off the toilet tank water supply valve, which can be located by following the water supply line at the lower left side of the tank. Turn the valve clockwise by hand.
Inspect the float ball for ruptures by lifting it up and down quickly. If you feel water sloshing about inside the float, it must be replaced. Turn the float ball counterclockwise to remove it from the threaded brass rod.
Allow the tank to fill completely. If the water overflows into the pipe, the new float ball will require adjusting.
Repeat Step 1 of Section 2 until the correct level is reached. Replace the tank cover.