One with inside info to leave before second drink (6)
I believe the answer is:
gossip
'one with inside info' is the definition.
(inside info can mean gossip)
'leave before second drink' is the wordplay.
'leave before' becomes 'go' (to go is to depart or leave. I am not sure about the 'before' bit.).
'second' becomes 's' (common abbreviation).
'drink' becomes 'sip' (sipping is a kind of drinking).
'go'+'s'+'sip'='GOSSIP'
'to' is the link.
(Other definitions for gossip that I've seen before include "'Rumours, scandal (6)'" , "Hearsay" , "Idle chat, tattle" , "Idle, malicious, chatter" , "Rabbit" .)