[drangundsturm]

A siphon will not work in vacuum, it takes external atmospheric pressure to push the liquid up the shorter leg.

So what happens in a vacuum? Gravity pulls the water out of the longer leg, then nothing replaces it so the process stops? Or nothing moves at all and it all holds together via surface tension? What if the long tube is so long or the tube such a wide diameter that the force of gravity overcomes the surface tension...

[Doe Eyes]

I think the problem with the water “boiling” (changes from liquid to gas) at 0 atmospheres. The expanding gas allows the water to fall back out of the tube.