The word syphon (, also spelled siphon) can refer to any device that conducts the flow of liquids through tubes. Used in the right way, the word refers to a tube in an upside-down U shape. The tube makes liquid flow up hill. It flows higher than the source of the liquid, to come out at a level lower than the surface of the source. The movement is done without pumps. It is powered by the fall of the liquid as it flows down the tube under the pull of gravity.