Dispenser to cop it, sadly (5)
I believe the answer is:
optic
'dispenser' is the definition.
(UK term for a measurement on a drinks container)
'cop it sadly' is the wordplay.
'sadly' indicates an anagram.
'cop'+'it'='copit'
'copit' anagrammed gives 'OPTIC'.
'to' is the link.
(Other definitions for optic that I've seen before include "Topic (anag.)" , "Device for measuring dispensed alcohol" , "Pub measure" , "Pub measuring device" , "of a viewer?" .)