A toilet flapper seals the tank fill hole to stop the rush of water into your toilet tank. This important part has to make a tight seal with the hole or the toilet will leak. Several different flapper sizes are available, so it is necessary to choose the right one. If your flapper is too small or too large it will cause a toilet leak.
A 3-inch flapper usually fits onto an older toilet. The 3-inch flapper still is sold commonly today and many toilets use this flapper, even some new model toilets. However, this flapper will not work if your toilet has a bigger fill hole and, therefore, your toilet will constantly fill and drain.
A 4-inch flapper is common on some newer model toilets. It generally fits only 4-inch diameter fill holes, and will not always form a tight seal on the 3-inch fill hole. Although, it is possible that the larger flapper does seal your 3-inch hole, this is not recommended. Standard, 4-inch flappers are widely available at all hardware stores and home improvement outlets, so it is best to buy the one that suits your toilet.
Odd Sized Flappers
Some special toilets require a special flapper. For instance, certain models and makes require their own flapper sizes to fit the specially sized fill hole. If you try to use a 3-inch or 4-inch flapper, the toilet will leak constantly. To find one of these special flappers, contact your manufacturer. Most manufacturers offer replacement parts right on their website. A plumbing supply outlet also may have access to these specially sized flappers.
Gallons Per Flush and Universal Flappers
Many flappers are sized by the gallon per flush rating of the toilet they service. Since the size of the fill hole is related directly to the number of gallons per flush (the fill hole has to drain so many gallons into the tank), many manufacturers use this measurement instead of inches. For instance, some flappers fit 1.6 gallon per flush toilets, which is the standard gallon-per-flush rating of toilets today. Universal flappers also can fit both 3- and 4-inch toilet drain hole sizes because of their unique shape. Many gallon-per-flush flappers have specific designs to fit any sized toilet fill hole.