Remove lid to drain jug (4)
I believe the answer is:
ewer
'jug' is the definition.
(thesaurus)
'remove lid to drain' is the wordplay.
'remove lid to' means to remove the first letter (in a down clue, the lid is letter at the top).
'drain' becomes 'sewer' (sewer is a kind of drain).
'sewer' with its initial letter taken away is 'EWER'.
(Other definitions for ewer that I've seen before include "Vessel for pouring" , "Container" , "from which liquid may be poured" , "Water-jar" , "Were (anag)" .)