Pythagorean Cup

A Pythagorean cup, also called a Tantalus cup, is a drinking vessel built as a practical joke that drains all of its contents through a hidden siphon in its base once it is filled past a certain level. Hero of Alexandria described the underlying siphon principle in the first century AD, and the oldest surviving example is a silver Roman cup from the late fourth century; the design continued to be refined through the medieval period and became a popular novelty item in European physics cabinets between the sixteenth and eighteenth centuries. The same siphon principle the cup demonstrates is used today in modern flush toilets and in the fabric softener dispensers of washing machines.