Drink in large draughts (5)
I believe the answer is:
quaff
'drink in large draughts' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for quaff that I've seen before include "Knock back" , "Imbibe" , "Drink deeply or eagerly" , "Drink enthusiastically" , "Drink in large draughts" .)