The Kowloon Cup is also known as the Fairness Cup or the Greedy Cup. It is called the Pythagorean Cup in Europe. It is said to have been invented by Pythagoras. According to Chinese legend, it was made by craftsmen of the Ming Dynasty[1]. When drinking from a Jiulong cup, as long as it is not filled to the brim, it is no different from a regular cup. If the pour is too full, the wine will flow completely from the bottom hole.

Nine Dragon Cup operates on the principle of siphon [2]. A faucet is erected inside the cup. There is a small hole at the bottom of the dragon neck, and there is also a hole outside the cup. There is a multiple pipe inside the dragon neck, and the upper part of the outer pipe communicates with the inner pipe. The outer pipe has a small hole in the cup. The small hole is the dragon. The hole at the bottom of the neck, and the inner tube connects to the hole outside the cup. If the water added does not exceed the upper opening of the inner and outer tubes, the cup is the same as the regular cup; if the water level exceeds the upper opening, the water will fill the space between the inner and outer tube walls, and the water will flow out completely through the inner tube.

https://www.youtube.com/watch?v=ppCigrmlu98