Bert's getting out the port (5)
I believe the answer is:
'the port' is the definition.
(I've seen this before)
'bert's getting out' is the wordplay.
'getting out' indicates an anagram (the letters get out of order).
'berts' anagrammed gives 'BREST'.
(Other definitions for brest that I've seen before include "French warships here in Brittany" , "Breton port" , "Naval base in Brittany" , "French port" , "Port in Brittany" .)