I’d make sure the tube is pretty wide. I made one and it wasn’t very impressive to wait 30 seconds while the water trickled out. Just seems like a leaky cup.
I’d go more for a toilet flush type of thing if I redid it.
The first cup took 90 seconds to drain about 200ml. The cross-sectional area of the tube in the second version is about 4.7x larger, so if my beginner-level understanding of Bernoulli's principle is accurate, I expect it to drain about 4.7x faster, so maybe it'll empty itself in 20 seconds instead of 90.
I think it can be slightly closer to you than that.
The cup is wider at the top than the bottom, which means when you tilt it over you are removing some liquid from a narrow part of the cup and adding an equal volume of liquid to a wide part of the cup. That means the level drops slightly.
Two phase flow is a difficult subject, so much so the owner of a nuclear engineering consultancy I worked for wrote his magnum opus on it: Two-Phase Flow in Complex Systems
It's imperative to get right in process environments like chemical production facilities and nuclear reactors.
https://www.wiley.com/WileyCDA/WileyTitle/productCd-04713296...
My grandpa had a similar contraption; a "puzzle jug" -- he'd fill it with wine, drink some, and pass it around to his guests -- who would often tip the jug and spill. Amusingly, potheads are more likely to succeed than the general population, because it's just a carburetor.
I know, because I always have to be very careful not to overfill it. But usually there is some leftower water in its pipe so it does not keep the fluid even if I not overfill - so nowadays I routinely take it apart and shake it dry before each washing - clever but not to convenient...
https://www.thingiverse.com/thing:123252
https://www.yeggi.com/q/pythagorean+cup/