Water seeks it's own level. If you put a pipe over another pipe with a gap between the outer pipe and the bottom, the level inside the outer pipe and outside the outer pipe will be very close to the same. If the inner pipe is shorter than the outer pipe, and is has an exit out the bottom, it will set the level in the tank. The only way water can get to the inner pipe is by flowing through the outer pipe. It goes up, but not above the water's surface.
If you want to go over the top, you use a siphon.
Originally Posted by Davi