If you need to change the flush valve of an American Standard Toilet, it will help to bring the part with you to the hardware store. There are at least 6 styles of flush valve or flaps. For one style, there are 3 unique shapes. For the style I am showing, there is a #4, #5 and a #6.
In many toilets, they will accept the universal flap style, but not all the American Standard.
If you have a toilet tank that is slowly leaking, causing the fill valve to turn on and refill the tank with water, you probably have to replace the toilet flap or flush valve. For the American Standard, if it has a circular rubber disc that lifts to flush the toilet, try to replace just this first. You should bring the part with you to the store to find a match; there are a couple different styles of this too. It will be connected by a screw or snap fitting.
