Drain drink slowly, darling (6)
I believe the answer is:
siphon
'drain' is the definition.
(thesaurus)
'drink slowly darling' is the wordplay.
'drink slowly' becomes 'sip' (I've seen this before).
'darling' becomes 'hon' (**).
'sip'+'hon'='SIPHON'
(Other definitions for siphon that I've seen before include "Draw off (liquid) by pipe" , "Squirting bottle found in shop" , "Tube drawing off liquid" , "Tube used to draw a liquid" , "On ship (anag)" .)