Never stopping, vessel guzzled by ancient drunk (9)
I believe the answer is:
incessant
'never stopping' is the definition.
(never ceasing)
'vessel guzzled by ancient drunk' is the wordplay.
'vessel' becomes 'SS' (prefix in ship names eg SS Great Britain).
'guzzled by' indicates putting letters inside (I've seen this in other clues).
'drunk' is an anagram indicator.
'ancient' anagrammed gives 'inceant'.
'ss' going into 'inceant' is 'INCESSANT'.
(Other definitions for incessant that I've seen before include "Continuous" , "Constant, unremitting" , "without a break" , "Endless" , "Since Stan was continual." .)