Apartment Toilet

It sounds like a Sloan, or similar, flush valve. Deppending on the make, you can sometimes get a new internal unit. It is more expensive than parts, but does not require any knowledge of how to repair it.: I see a lot of diagrams on the workings of toilets but it is always the toilets with the tank in the back. I have a toilet in an apartment that is the kind shaped like a T with a handle on one side and a knob on the other, a pressurized flusher. Are there any diagrams of these on line. The toilet keeps flushing on its own and it flushes too long and fills the tank too much when it does flush.