You need to be more explicit about what you don't understand. With a toilet flush the design objective is the following: * There is a cistern full of water;

You need to be more explicit about what you don't understand. With a toilet flush the design objective is the following: * There is a cistern full of water; * You press a button; * The entire cistern flushes the toilet, even if you release the button; * After the flush, the cistern re-fills. There are multiple mechanisms to accomplish this, but usually you would simply buy a mechanism and fit it according to its design. So ... what don't you understand? (Noted: I'm not a plumber, I'm not an expert, I'm just trying to understand your question)