Drink, when you urge to, squash (8)
I believe the answer is:
suppress
'to squash' is the definition.
(I've seen this before)
'drink when' is the wordplay.
'drink' becomes 'sup' (I've seen this before).
'when' becomes 'press' (I can't explain this - if you can you should believe this answer much more).
'sup'+'press'='SUPPRESS'
'you urge' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for suppress that I've seen before include "Crush, put down" , "Stifle or overpower" , "Stop publication of" , "Stifle, feelings or rebellion" , "Prevent the dissemination of, information say" .)