Your toilet's flushing power depends on the water leaving the tank and rushing into the bowl. When not enough water is leaving the toilet's tank with each flush, the toilet's flushing power is reduced, which may lead to clogs.
A toilet's flapper controls how the water from the toilet's tank flows into the toilet bowl. The flapper seals off the large drain hole in the bottom of the toilet's tank. When you push down on the toilet's handle, the handle pulls up an attached arm inside the toilet tank. The arm pulls on a chain that attaches to the top of the flapper, allowing the water to drain out of the tank. The flapper closes over the drain when the water in the tank drops to a certain level, and then the toilet's tank refills with water in preparation for the next flush.
Testing the Flapper
If you think the toilet tank is not letting enough water out with each flush, test the flapper to see if it is defective. Remove the tank lid and set it aside somewhere it will not crack. Flush the toilet once the toilet has fallen completely silent, and then watch the flapper carefully. The flapper should not fall back over the tank's drain hole until at least 80 percent of the water in the tank has drained out, or else the toilet's flushing power can be reduced. If the flapper closes over the drain hole too early, you need to either adjust it or replace the flapper with a new one.
Some flappers come with a float that attaches to the flapper's chain. The float helps determine how long the flapper stays open. Sliding the float down to a lower portion of the flapper's chain keeps the flapper open longer, since the float pulls up on the flapper until the water dips below the level of the float. If the flapper does not have a float on the chain, you may adjust the chain itself to prevent the chain binding up, which can affect the flapper's performance. If you slide the chain off the hook on the arm and slide a different link onto the chain so the chain has only two or three links of slack, the chain is less likely to bind up.
Replacing the Flapper
Ultimately, if adjusting the flapper does not allow more water to leave the toilet tank with each flush, you must replace the flapper. When the flapper's material wears out, the flapper takes on water or becomes water-logged. Instead of floating in the tank when you flush, the flapper falls more rapidly back over the tank's drain hole. You must close the toilet's water supply valve on the wall before you remove the old flapper or the toilet will run continuously until you put in the replacement. You also must install a new flapper that matches the old one exactl, or the flapper can leak water.