Drop jug back in as a goodbye (8)
I believe the answer is:
farewell
'a goodbye' is the definition.
(I've seen this before)
'drop jug back in' is the wordplay.
'drop' becomes 'fall' (synonyms).
'jug' becomes 'ewer' (type of vessel).
'back' shows that the letters should be reversed in order.
'in' is an insertion indicator.
'ewer' written backwards gives 'rewe'.
'fall' placed around 'rewe' is 'FAREWELL'.
'as' is the link.
(Other definitions for farewell that I've seen before include "Goodbye, hope you get on" , "Wish on leave-taking" , "Cape at the southernmost point of Greenland" , "Archaic goodbye or leave-taking" , "All the best" .)