A device used to move a liquid from a container, over an edge higher than the level of the liquid, down to a lower level. A curved tube is put into the liquid, and some form of mechanical force is applied to start the liquid flowing through the tube. A suction is often put on the end of the tube to start the liquid flowing.

When the flow is started, atmospheric pressure forces the liquid from the higher container into the tube, and the weight of the liquid flowing through the tube to the lower level keeps the liquid flowing.