Have you ever seen those dog watering bowls that automatically refill using an inverted water tank? The vacuum keeps the water in the tank even though the tank water level is higher than the dish. But when the dog drinks the water, the water empties out and the net force keeping the water in the tank changes and so water leaves the tank and goes into the dish. I want to make something like this but with an open top so it can be easily refilled or other water tanks added. I want to keep the design simple, no electricity or expensive pieces of equipment. The build should also be relatively simple. Any suggestions?