Bum quaffing new port (6)
I believe the answer is:
nantes
'port' is the definition.
(I know that Nantes is a port)
'bum quaffing new' is the wordplay.
'bum' becomes 'nates' (anatomical term for the buttocks).
'quaffing' means one lot of letters goes inside another (to quaff is to drink or consume).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'nates' going around 'n' is 'NANTES'.
(Other definitions for nantes that I've seen before include "Port city in western France" , "port abroad" , "City and port of W. France on the Loire" , "Port city on the Loire estuary" , "Site of historic drownings" .)