The cup of Pythagoras

Drinking has to be learnt: The Pythagorean cup - also known as the cup of moderation or Tantalus cup - is a drinking vessel that requires the user to drink in moderation.
Due to its ingenious design, the cup can only be filled up to a certain height. This allows the modest user to savour their drink in peace. However, if he is greedy and pours himself over the fill line, the entire contents spill out through a hidden hole in the base of the cup onto his lap. That's what he gets...