How to Repair a Running Toilet. So your toilet goes through more water than Niagara Falls? Most likely the problem is the ball cock's diaphragm or the tank flap, so stop jiggling the handle and roll up your sleeves. Here are a few easy steps to fix your toilet.
Identifying the Source
Remove the toilet-tank lid and place it out of the way on the floor.
Investigate the ball cock. It's a valve attached to the float (which is either a metal or plastic ball on the end of a long rod or a plastic canister that slides up and down a vertical plastic pipe). If you can see or hear water coming from this valve, it may need to be cleaned or replaced.
Reach down into the bottom of the tank and press down on the edges of the tank flap (a black or red rubber cone that fits into the tank's hole). If the sound of water running into the bowl stops, you know that the flap may be deformed or worn from age and needs to be replaced.
Get ready to work. Turn off the water supply for the toilet (this valve is most often found coming out of the floor or wall near the toilet; turn the handle in a clockwise direction). Flush the toilet to drain some of the water and make the work easier.
If you need to replace the diaphragm or tank flap, take it with you to a hardware store or plumbing supply house to make sure you buy the correct replacement.
Cleaning or Replacing the Ball-Cock Diaphragm
Snap off the cover of the ball cock and put it out of the way.
Remove the four screws holding down the top plate of the ball cock, using a screwdriver. The float-control arm is attached to this and may be spring-loaded. You'll see a rubber diaphragm.
Remove the diaphragm carefully, noting which side is up, and check its condition. Sometimes a piece of gravel or rust or a hard-water deposit can get lodged under the diaphragm and cause a leak, or the diaphragm can become misshapen or worn through with age.
Replace the diaphragm or clean it by rinsing it in the tank's water; flush the valve itself by turning on the water supply for the toilet just enough to get a flow of water for a couple of seconds.
Replace the top plate and secure it with its screws.
Turn the water supply back on, allowing the tank to fill, and replace the lid.
Replacing the Tank Flap
Remove the tank flap. Some have a clamp-type assembly, while others hook to short posts that stick out from the overflow pipe; all attachments are fairly easy to remove by hand.
Install a new tank flap.
Turn on the water supply and replace the lid.