Older American Standard toilets use a part called an actuator to regulate the flow of water from the toilet's tank to the bowl. An actuator functions somewhat like a flapper valve in toilets of today, but with a few differences that allow more water to drain out of the toilet's tank with each flush.
Similar to a Flapper
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An American Standard toilet actuator works like the flapper valves in modern gravity-flush toilets. The actuator attaches to the arm on the backside of the toilet's handle, which uses a chain to move the actuator. The actuator lifts up, opening the drain hole in the bottom of the toilet, letting the water rush into the bowl and flush the waste down the drain.
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Design
A toilet actuator has one tube that attaches to the bottom of the toilet's tank with a hinge. The first tube connects to a second tube below it. On the bottom of a second tube is a rubber seal that stops up the drain hole in the bottom of the toilet's tank. A chain attaches to the top tube, pulling the actuator up and back so the water can exit the tank. Toilets with an actuator have a shorter arm attached to the handle, since the arm does not need to pull the actuator straight up.
Leaking Actuators
When an actuator leaks, the toilet's tank will leak water and then refill constantly, just as when a flapper begins to leak. The rubber seal on the bottom of the actuator assembly will wear out the same way a flapper valve does and must be replaced. Some rubber seals snap on and off the bottom of the actuator, while others attach with a screw. You may need to hold the nut on the other end of the screw stationary, using needle-nose pliers.
Sticking Actuators
Sometimes an actuator will not fall back down over the drain hole in the bottom of the tank, sticking in the open position. Normally, the actuator stays seated until the chain raises it. The water around the actuator will keep the top tube floating and the actuator open. Once the water around the top tube drains out of the tank, the tube will no longer float, and so the actuator will fall back down over the drain opening. Debris will clog the drain hole in the top tube, keeping it from sensing that the water around it has drained out, and in turn keeping the actuator open. Cleaning out the hole in the tube should stop the sticking problem.