The flapper valve is what regulates water to the bowl. It is important that flappers are sized appropriately to maintain a proper seal needed for the toilet to both flush properly and control the flow of water to the bowl. Most toilet flappers are either a 2" or a 3" depending on the size of the drain opening from the tank to the bowl. When choosing a replacement flapper you will have to know what you currently have:
Flapper Style: Flexible Rubber or Solid Plastic Frame
Size: Either 2" or 3" (pre-1994 toilets are usually 2")
Flushing Capacity: 5 , 3.5 , 1.6 , or 1.28 gallon per flush toilet
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