Drank excessively back in storeroom (5)
I believe the answer is:
depot
'storeroom' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for depot that I've seen before include "Toped (anag.)" , "Storage place" , "Place where buses and trains are kept" , "Headquarters - storehouse" , "Large storage site" .)