Supple soldier dipping into drink (5)
I believe the answer is:
agile
'supple' is the definition.
(I've seen this before)
'soldier dipping into drink' is the wordplay.
'soldier' becomes 'GI' (term for US soldier).
'dipping into' is an insertion indicator.
'drink' becomes 'ale' (type of beer).
'gi' put inside 'ale' is 'AGILE'.
(Other definitions for agile that I've seen before include "Moving quickly and easily" , "Mentally acute" , "Nimble on the feet" , "Quick and easy-moving" , "Nimble, supple" .)