Drank heavily back in warehouse (5)
I believe the answer is:
depot
'warehouse' is the definition.
(I've seen this before)
'drank heavily back' is the wordplay.
'drank heavily' becomes 'toped' (I've seen this in another clue).
'back' is a reversal indicator.
'toped' reversed gives 'DEPOT'.
'in' is the link.
(Other definitions for depot that I've seen before include "Storehouse as for supplies" , "Store for large quantities" , "Military HQ" , "Wherein bus drivers" , "Bus station in the US" .)