My goal was to make a version of the pythagorean cup that:

• looks like a real (mediaeval or so) goblet
• hides the siphon mechanism inside the walls of the cup
• drains the water very quickly after reaching the “magical line”

How to get the best results

1. Place the goblet on a level surface.
2. Gently fill in the water, otherwise it might splash up the tubes in the siphon and cause it to run even-though the water level is still beneath the line.
3. I'd recommend using a hydrophobic polymer (for example PLA) for this print, so the water does not get “stuck” in the tubes after emptying. 

How this works

The main principle behind this is the siphon. It allows a liquid to flow upwards a bit without being actively pumped up. But since the laws of thermodynamics (sadly) also apply to the siphon, the liquid doesn't just flow up on its own. The tube trough wich the water flows must end at a point where the liquid has a lower gravitational potential, meaning, if you look on the syphon as a whole, the liquid travels downwards in total. 

The pythagorean cup now makes use of this in a very smart way. When you start filling the cup, the water level in the cup rises, thus the water level in the tubes that connect the cup with the outlet at the bottom also rise by the same amount because of the principle of  communicating vessels. Once the water level is high enough, the siphon activates because the water now flows into the falling part of the tube and sucks the contents of the goblet out. 

What it looks like on the inside

Here, you can see a cross section of the goblet. I tried to fit in as many pipes as possible, so the water drains faster.

There are 15 pipes (marked in orange) going up and 15 going down. In the foot of the goblet the pipes lead to a chamber, at the bottom of which they get split up again and leave the goblet at the sides. 

If you have any questions about this model, please feel free to ask.