Drain head off jug of beer perhaps (4)
I believe the answer is:
ewer
'jug of beer perhaps' is the definition.
I can't tell whether this defines the answer.
'drain head off' is the wordplay.
'drain' becomes 'sewer' (sewer is a kind of drain).
'head off' means to remove the first letter.
'sewer' with its initial letter taken off is 'EWER'.
Can you help me to learn more?
(Other definitions for ewer that I've seen before include "A wide-mouthed water-jug" , "Were (anag)" , "A wide-mouthed water jug" , "from which liquid may be poured" , "Sort of jug" .)