The inner workings of the tank flushing system comprise the guts of a toilet. Replacing these components basically involves the use of common household tools coupled with a visit to your local plumbing supply, hardware or home improvement store to obtain the replacement parts. The key is knowing what to replace, and when.
Replace The Flapper
Shut off the water supply to the toilet. The shut-off valve is normally found to the left of the toilet, either coming up from the floor or on the wall, approximately 6 inches high. To shut off the water, turn the valve completely clockwise. Remove the tank lid. Flush the toilet and hold down the handle to remove the most amount of water from the tank. Note the length on the chain, from the flapper to the flush lever. Remove the chain from the flush lever.
Put on rubber gloves and remove the flapper, if the flapper is deteriorated or damaged. Either slide the flapper up and over the overflow tube, or remove the flapper ears from the overflow tube or the pins of the flush valve. Write down the toilet manufacturer and model number. Take this information along with the old flapper to purchase a replacement flapper.
Install the replacement flapper depending on your toilet's flush system. Slide the collar, or ring, of the flapper over the top of the overflow tube and slide the flapper down the overflow tube, making sure the flapper seats fully on the flush valve opening. Or, cut the collar along the line marked "cut," using a utility knife, and slip the flapper ears over the pegs on the bottom of the overflow tube. Or slip the flapper ears over the pins of the flush valve.
Attach the flapper chain to the flush lever. Turn the shut-off valve counter-clockwise, to turn on the toilet's water supply. Flush the toilet to make certain the flapper operates properly.
Replace The Ball Cock
Replace the ball cock if the water continues to run even after the water level reaches the top of the overflow tube, and slightly adjusting the arm lever on the float ball does not stop it. Shut off the water supply, turning the shut-off valve completely clockwise. Remove the tank lid and flush the toilet. Hold down the handle to remove as much water as possible, and absorb any remaining water with a towel.
Unscrew the supply hose's connecting nut where the supply hose connects underneath the tank. Grip the nut at the base of the ball cock, using pliers. Loosen the locknut underneath the ball cock, using the wrench. Unscrew the locknut and lift the ball cock from the tank.
Clean around the opening where the new ball cock will be installed, using an emery cloth. Install the new ball cock assembly. Tighten the locknut underneath, being sure not to over tighten and possibly crack the tank. Connect the refill tube, that goes from the ball cock assembly, to the top of the overflow tube. Connect the supply line underneath the tank. Turn the shut-off valve counter-clockwise to reopen the water supply and check for any leaks.
Replace The Flush Valve
Stop a leak from a corroded overflow pipe that is causing the tank's water level to lower and the ball cock to constantly keep allowing water into the tank. Replace the entire flush valve assembly. Shut off the toilet's water supply by turning the shut-off valve completely clockwise.
Remove the tank lid and flush the toilet, holding down the handle to remove all the tank water. Use a towel to absorb the remaining tank water. Place a second towel on the floor nearby. Detach the tank from the bowl, removing the tank-to-bowl bolts with a screwdriver on the bolts and a wrench on the nuts underneath.
Place the tank on the towel on the floor. Remove the large, spud gasket on the bottom of the tank, then remove and replace the flush valve assembly. Place the spud gasket back onto the bottom of the tank and place the tank back atop the bowl. Install new tank-to-bowl bolts, including new rubber and metal washers, along with the nuts.
Turn the shut-off valve counter-clockwise, in order to turn on the toilet's water supply. Check around the toilet for any possible leaks, and tighten any nuts accordingly. Be sure not to over tighten.