Replacing a toilet flapper is not a hard job at all. Unhook the chain from the toilet tank lever and remove the flapper from the fill tube. Some types have an assembly that slides over the fill tube.
Not sure if you have a problem with your toilet flapper? See the article, 'Fixing Toilet Tank Issues' or 'Fixing and Troubleshooting Toilet Problems' for a complete listing of all the subjects related to toilet repair.
Before you can replace your flapper, you will need to purchase a new one.
Purchasing a Toilet Flapper
Toilet flappers can be ordered online or are available at home supply stores. Most of them are universal and vary only by size.
A toilet flapper is not an expensive item. You should be able to find one for around ten dollars, although some may cost more. For a premium toilet, you may have to obtain an particular flapper that is matched to the toilet, these will likely cost more.
Getting the Right Size
In the past flappers were pretty universal. With the new water saver toilet requirements (all new toilets are required to use 1.6 gallons of water), there have been some engineering changes. Many of the newer toilets have a 3" diameter outlet for the flush valve, instead of the 2" that was standard for many years.
For a long time all toilets were manufactured using a 2" outlet for the flush valve. Most flappers would handle this opening size as long as the opening did not exceed 2 1/2" or so. There has to be enough of a flange around the opening for the flapper to properly seal. If there isn't, the toilet will leak water into the bowl and the tank will need to refill periodically.
Check the size of the existing flush valve outlet before getting a replacement flapper. Lift the flapper up and measure the inside diameter of the outlet. Should be either 2" or 3". Purchase the appropriate replacement part.
For universal replacement flappers, you can get a 2" or a 3". If your toilet has been installed since 2000, it is likely that you will need a 3" flapper. Prior to that time, the 2" will likely work. If you want to be sure, take the old flapper with you when you go shopping.
Installing a Toilet Flapper
Before you can install the flapper, you will need to shut off the water to the toilet. Flush the toilet to drain most of the water out of the tank. Take the lid off the toilet tank to see the flapper location. A little water in the bottom of the tank is okay and will not interfere with the installation.
Attaching the Flapper to the Flush Valve
The flapper should attached to plastic wings on either side of the fill tube. The flapper is made out of rubber, so there are two flaps with holes in them that go onto the side of the flush falve.
Near the bottom of the flush valve you will see two ears that protrude out the sides. The flapper presses on and off these ears. Pull the old one off and then put the new one on over the two ears. Make sure it is moving freely up and down.
The new flapper should completely cover the rim of the flush valve with some over hang. If the edge of the flapper appears to be too close to the edge of the flush valve opening, you may have gotten the wrong flapper.
Hooking Up the Pull Chain
For the flapper to work, it needs to be attached to the arm on the toilet handle. This is done via a chain that is either metal or plastic. The chain should be hooked to the new flapper already.
There will be a clip that holds the old chain onto the arm of the toilet handle. Remove the clip and remove the old chain. Attach the new chain with the new clip.
You want some slack in the chain, but not too much. If the chain is too long, it will tangle and cause the flapper not to open or not close. See the article, 'Adjusting a Toilet Handle Chain' for infomation on getting the chain located properly.
Test the Flapper
After you have installed the new flapper, turn the water to the toilet back on. After the tank fills, flush the toilet a couple of times to make sure the flapper is opening and closing correctly. Check to make sure that there is no interference from the chain.
Replacing a flapper is a pretty simple job. You just need to make sure that you get the right one for your toilet. Most of the time this will be either a 2" or 3" flapper. While you are working in the tank, you should check to make sure that the toilet tank water level is set to the right height. See the article 'Setting Toilet Tank Water Levels' for instructions.