Three-out

[Quizmonster]

It has disappeared now, but there was a question here about a child in Birmingham fetching drinks and having to ask for a "three-out". I seem to remember that it got only one answer which wasn't really an 'answer', if you see what I mean.
At the time, I had no idea what it meant either, but - purely by serendipity, whilst researching other meanings today - I came upon the following in The Oxford English Dictionary...
"Three-out, a glass holding a third of some measure of liquor."
It goes on to explain that an order such as, "Two Bass's and three outs" meant two bottles of Bass shared equally among three separate glasses.

I just hope the original poster sees this and my apologies for posting an answer instead of a question!