Small jug found in drain (5)
I believe the answer is:
sewer
'drain' is the definition.
(I know that sewer is a type of drain)
'small jug' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'jug' becomes 'ewer' (type of vessel).
's'+'ewer'='SEWER'
'found in' acts as a link.
(Other definitions for sewer that I've seen before include "Filthy channel" , "One plying needle; drain" , "Underground drain" , "Conduit for carrying away waste matter" , "Needlewoman" .)