Siphoning is based upon the principle that once started, liquid will continue to flow out of a container through a tube as long as the discharge is lower than the intake. It's how some young miscreants got gas for their cruisers before locking gas caps were standard
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*only read on if you want to understand the siphon principle*
Basically the atmosphere presses down on the surface of the water at approximately 7lbs/square in. When you put a tube in the water and generate a vacum in the tube, the atmospheric pressure causes the water to travel up through the tube (like a drinking straw). Now if you place the discharge end of the tube below the intake, gravity will pull the liquid down out of the tube. The liquid being pulled out of the tube by gravity will continue to generate the vacuum and thus pull more liquid up and out of the container.
