at a draft—drink all of smth. during one continuous action of swallowing:
- He drank half a pint of beer at a draft.
on draft—(usually of beer) served from a barrel and not sold in bottles:
- We had no beer on draft and a handful of bottled beers.
at a draft—drink all of smth. during one continuous action of swallowing:
on draft—(usually of beer) served from a barrel and not sold in bottles: