What do you call that?

The bowl they bring you to wash your tableware in China.  When I ask restaurant staff for another one (to pour more tea out, wash a late arrival's tableware, or whatever), I never know what to call it.  If I ask for a "bowl" (碗), I get another food bowl.

I'm talking about the bigger, plastic or glass bowl.  This is a very minor question, but it's driving me crazy because I keep forgetting to find out... until I'm at a restaurant again.  And then I just have to describe it to them until they figure out what I'm asking for.  :-/

Thank you,

George