A Pythagorean cup (also known as a Pythagoras cup, a Greedy Cup or a Tantalus cup) is a form of drinking cup which forces its user to imbibe only in moderation. Credited to Pythagoras of Samos, it allows the user to fill the cup with wine up to a certain level. If the user fills the cup only up to that level he may enjoy his drink in peace. If he exhibits gluttony, however, the cup spills its contents out the bottom (the intention being: onto the lap of the immodest drinker).

https://en.wikipedia.org/wiki/Pythagorean_cup