At home, locate the shutoff valve on the wall near the toilet and turn it off. Next, take the cover off the tank, so you can see inside. Flush the toilet to empty the tank. If the tank starts to fill again, you haven’t turned the shutoff completely off.
Angie's How To replace your toilet flapper
A toilet flapper is the rubber plug inside the tank that lifts when you flush, allowing water to flow in to rinse and then fill the bowl. Over time, the flapper gets old, cracks and allows the toilet to run by failing to fully seal against the valve seat.
A properly functioning flapper cuts down water bills and obnoxious noises from constant filling, but calling a plumber could cost anywhere from $50 to $200 depending on where you live. Luckily, you can replace this roughly $10 part in five easy steps:
The flapper sits on the very bottom of the tank. First, detach the chain from the metal or plastic tank lever arm connected to the handle. Next, reach in and twist the flapper from side to side until it comes loose. If a ring around the fill valve holds the flapper in place, then slide it all the way up and off.
Don’t throw the old flapper away just yet. Take it to the hardware store to ensure you get the right replacement.
Toilet flappers come in three common types: rubber, seat disk and tank ball. Newer toilets normally have rubber flappers, while older toilets have seat disc flappers that you screw on or snap into place. A tank ball, also found on older toilets and attached via a lift wire, looks exactly like you would expect.
You should be able to find the right flapper at your local hardware store based on the approximate age and brand of your toilet. Compare the replacement to the old flapper. If you’re unsure, ask an employee who is trained on plumbing products.
Depending on the type of flapper, either snap, drop, screw or slide the new one into place. If the new flapper comes with a ring on the end, but small hinges connected the old one, you should cut the ring off first and attach it the same way.
Make sure the chain is long enough to allow the flapper to seal. It should have some slack, but not enough that it catches underneath the flapper. If necessary, remove a few links before attaching it to the tank lever arm.
With the new flapper installed, turn the shutoff valve on. When the tank is full, flush it to make sure that the flapper seals when it starts to fill again.
If it runs a little bit, empty the tank again. Make sure the flapper is properly seated on the bottom of the tank and the chain is not too long. Turn the water on and try again.
When you’re certain the flapper seals, put the cover on and give yourself a pat on the back. Brag to your friends or don’t, since they might ask you to replace theirs.
If the toilet continues running or you discover that the entire toilet — not just the flapper — needs replaced, look for highly rated plumbers on the List.