Keep drug in cook's vessel (8)
I believe the answer is:
stockpot
'cook's vessel' is the definition.
(I've seen this before)
'keep drug' is the wordplay.
'keep' becomes 'stock' (I've seen this before).
'drug' becomes 'pot' (pot is a kind of drug).
'stock'+'pot'='STOCKPOT'
'in' is the link.
(Other definitions for stockpot that I've seen before include "stew" , "Slow cooking vessel" , "gravy container" , "Cooking vessel for soups" , "Container holding base or raw material for soup" .)