A siphon is a way of draining a tank at a high level from the top to another one at a lower level. The tank is not drained from the bottom but by a tube that exits the upper tank from the top and then turns downward to the lower tank. Or it could be from the side as long as one part of the tube goes above the liquid surface of the top tank. Surprisingly the liquid will move upward against gravity, a feat not possible in the world of solids. This is due to low pressure that keeps the liquid in the top part of the siphon from falling and the connection between fluid particles that pressure provides.