have a hollow leg
Meaning:
Have a large thirst (for alcohol) or, sometimes, have a large appetite 酒量很大；胃口很大
Example:
You think you can drink him under the table? You're joking! He's got a hollow leg. 你以為你能灌醉他啊?開玩笑!他可是海量。
Origin:
Drinking large amounts (while remaining clear headed) has a very long history. The origin of this very colourful expression is self-evident: it's as if a person were pouring all that drink into a bottomless well.