Siphon

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A siphon (from Ancient Greek σίφων (síphōn) 'pipe, tube'; also spelled syphon) is any of a wide variety of devices that involve the flow of liquids through tubes. In a narrower sense, the word refers particularly to a tube in an inverted "U" shape, which causes a liquid to flow upward, above the surface of a reservoir, with no pump, but powered by the fall of the liquid as it flows down the tube under the pull of gravity, then discharging at a level lower than the surface of the reservoir from which it came. That is a gravity siphon, but it is not the only kind. There are two leading theories about how gravity siphons cause liquid to flow uphill without being pumped and powered only by gravity. The traditional theory for centuries was that gravity pulling the liquid down on the exit side of the siphon resulted in reduced pressure at the top of the siphon. Then, atmospheric pressure was able to push the liquid from the upper reservoir, up into the reduced pressure at the top of the siphon...

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