Replacing the flapper seal on a toilet flush valve is an easy task that most people will have to contend with. Many constant running water problems can be solved by replacing this seal, as well as some toilet tank leaks.
Step 1: Turn Off the Water Supply
In order to prevent water damage to the floors and surrounding areas turn the water supply lines off before beginning. These can usually be found behind the toilet next to the floor, but in some cases the main water shutoff may have to be turned off.
Flush the toilet a couple of times and then use dry towels to soak up the remaining water within the toilet tank.
Step 2: Remove the Flapper
Remove the flapper chain, or plastic strip, from the flapper and force it from the posts that hold it in place. Slide it out and clean the area inside the reservoir where the flapper rests.
Step 3: Install the New Flapper
Trim the new flapper to size with a razor blade and slide it back into place. Re-attach the chain, or plastic strip, and adjust until the flapper closes properly.