If you haven't read my last 2 blog posts, you should. They both directly relate to what I'm talking about in this one.
Alternatively, if you have even the slightest understanding of fluid dynamics, you don't need to read my last 2 posts.
In reality, if you've never even thought about fluids, you don't need to read my last 2 posts, because this is actually pretty simple, especially when compared to what we've done in class this year.
Right now, our goal is to get fluid from one cup into another. We could just pick up one cup and pour it into the other, but that's boring, and not very easy to do with large amounts of liquid. We could just scoop it out of one cup and dump it into another over and over, but that's boring and time-consuming. We could just pray to the old gods, but that also comes with its own drawbacks. So what are we going to do? We're going to siphon it through a tube.
Now take a look at the following gif.
The fluid from the left cup is transferring into the right cup, until they equalize to one height. If we wanted to transfer all of the liquid, we could just put the right cup at a lower level.
The issue with siphoning like this is that we can't just drop one end of a tube in each cup and expect it to work. If the tubes were connected from the bottoms, this wouldn't be an issue.
In this case, the transfer had to be jump-started, so the fluid travels up-hill into the tube, before it falls back down, and begins dragging more fluid with it.
One way to jump-start the transfer is to submerge one end of the tube into the left cup, then suck on the right end a little bit so the fluid starts to flow into the tube, and passes the highest point in the tube. Then, stop sucking, and put the end of the tube into the other cup, and as the fluid falls, it will drag more with it.
Another way is a little more tricky, but also more clean. It starts the same, with one end of the tube submerged in the left cup. Then, bend the tube so that it goes down out of the left cup, then back uphill, like a "u". Then, pour a decent amount of liquid into the "u". After, while making sure the part of the tube in the left cup stays submerged, put the other end of the tube facing down into the right cup, so the liquid starts pouring out. When the liquid starts pouring out, it'll drag more behind it, and eventually out of the left cup.