Skilful Bill drained pint without spillage in the end (5)
I believe the answer is:
adept
'skilful' is the definition.
('adept' can be a synonym of 'skilful')
'bill drained pint without spillage in the end' is the wordplay.
'bill' becomes 'ad' (advertisement stuck on wall**).
'drained' means to remove the middle letters.
'without' is an insertion indicator ('without' can be similar in meaning to 'outside').
'in the end' says to take the final letters.
'pint' with its centre removed is 'pt'.
The last letter of 'spillage' is 'e'.
'ad'+'pt'='adpt'
'adpt' enclosing 'e' is 'ADEPT'.
(Other definitions for adept that I've seen before include "Taped (anag.)" , "Very skilled/proficient" , "Skilful, expert" , "Proficient - expert" , "Highly proficient" .)