Many trick vessels work by concealing air pipes and water channels inside the walls or base so that liquid behavior appears self-caused to an observer who cannot see the plumbing. The effect depends on routing flow through chambers invisible from the outside, not on any novel physical force.
Devices regulate their own operation by letting a rising or falling float trigger valves, and by using the siphon to start or stop flow automatically once a liquid reaches a set level. Automatic behavior is achieved by tying the trigger to the water level itself rather than to an external operator.
Several vessels exploit sealed pockets of air whose pressure changes as water enters or leaves, pushing liquid upward or holding it back on command. Enclosing air in a fixed cavity turns the compression of that air into the working force that drives the display.