Directions returning soldier to drink (4)
I believe the answer is:
swig
'to drink' is the definition.
(I know that swig is a more specific form of the action drink)
'directions returning soldier' is the wordplay.
'directions' becomes 'sw' (I've seen this in other clues).
'returning' is a reversal indicator.
'soldier' becomes 'GI' (GI can mean a US soldier).
'gi' reversed gives 'ig'.
'sw'+'ig'='SWIG'
(Other definitions for swig that I've seen before include "Swallow (drink) greedily" , "Drink quickly from bottle" , "Drink deeply" , "Slug" , "Large draught of drink" .)