Toilet flapper valves can eventually wear out from repeated use. A flapper may not seat in the bottom of the toilet tank and may cause a toilet to run and waste water in the process. Replacement toilet flappers are available in plumbing stores and home improvement stores. Take note of your type of flapper before going to the store so that you can purchase a replacement that fits your system.
Turn off the toilet water supply valve. The valve is on the wall or floor near the base of the toilet. Turn the knob clockwise to shut off the valve. If the valve is stuck and will not turn, spray it with a lubricant to loosen. If the knob is persistent and will not turn, turn off the main water supply valve to the house.
Remove the cover to the toilet tank by lifting it straight up; set it aside. Flush the toilet so that the water in the tank evacuates. If your toilet flapper connects to the refill tube on the left with a chain, remove the refill tube from inside of the overflow tube.
Remove the chain from both the flush lever and the flapper. There is a small snap on each end that fastens the chain to the flush lever and the flapper. Pinch the snap to release the chain ends. If either end of the chain is missing its clip, you may use needle-nose pliers to remove the chain.
Grasp the flapper firmly on each side and pull it straight up and off the top of the overflow tube. Place the new flapper over the overflow tube and press it into the bottom of the toilet tank. Center the flapper so that it fully covers the valve opening in the tank bottom.
Attach a new chain to the flapper by pressing the snap to open it and hooking it on the flapper ring. Attach the other end of the chain to the flush lever in the same manner. Replace the refill tube inside of the overflow tube. Turn on the toilet water supply valve.
Flush the toilet and watch it function to make sure that the handle pulls the flapper high enough to open the bottom valve. Also, check to see that the flapper seats itself on the valve to close it after flushing.
If the toilet flapper is not closing fully on the tank valve, you will hear the toilet running and it will not shut off. Adjust the chain on the flush lever to make the chain length longer so the flapper closes all of the way. If the chain is too long, the flapper will open the valve only part way and will not provide efficient flushing and evacuation of the toilet bowl. In this case, shorten the chain on the flush lever. It is advisable to buy a new toilet chain each time you replace a flapper. The chain and flapper usually last about the same amount of time.