1. The problem statement, all variables and given/known data If you have a water tower (basically a cup) open to the atmosphere, with a siphon (basically a straw) inside it as shown below: (sorry assume the height h extends to the bottom of the cup instead of only part way - would that change anything though?) Then what is the maximum height at which you could have "y" to still drain the cup? 2. Relevant equations p = po + pgh 3. The attempt at a solution So my understanding here is that you have the pressure exerted by the atmosphere and the pressure exerted by the water here, which depends on depth. Since the water pressure only depends on height, even though the straw is outside of the water tower, at a depth H, there will still be a pressure pgH pushing down on the water. The trouble is then, how to push the water up the height Y. That's entirely dependent on the atmospheric pressure right? Thas the only other force / pressure source i can see acting here. So since atmospheric pressure is equivalent to 10m of water, the max Y could be would be 10m i believe. Am i on the right track here?