Regular's drunk last of beer on tap (6)
I believe the answer is:
patron
'regular's' is the definition.
(I've seen this in another clue)
'drunk last of beer on tap' is the wordplay.
'drunk' indicates an anagram.
'last of' suggests the final letters.
The last letter of 'beer' is 'r'.
'r'+'on'+'tap'='rontap'
'rontap' anagrammed gives 'PATRON'.
(Other definitions for patron that I've seen before include "With help, he" , "manager (13) [FRENCH]" , "Sponsor or backer as of the arts" , "Sponsor or supporter as of the arts" , "Pot ran out for protector" .)