Buyer gets half the purest second drink (9)
I believe the answer is:
purchaser
'buyer' is the definition.
(synonyms)
'half the purest second drink' is the wordplay.
'half' means to take half the letters.
'second drink' becomes 'chaser' (I've seen this before).
'purest' halved is 'pur'.
'pur'+'chaser'='PURCHASER'
'gets' is the link.
(Other definitions for purchaser that I've seen before include "customer" , "I'll buy" , "Buyer" , "Shopper" , "Punter" .)