American Standard seat disks. Older American standard toilet have an actuator in place of a flapper. it looks like a big black thing with a round tube on top that the chain attaches to, when you flush this toilet the actuator seams to lay on it's back for a few seconds and then drops back down, and the tank refills. On the bottom of this actuator is a rubber disk, this disk is what you need to replace, there are two kinds of disks, one snaps on and the other screws on. most stores sell a disk that can be used for either. Screw or pull the old one off (this is a very dirty job The black comes off on to your hands) clean the seat and put the new one on, test a few times. You are done.