I'll manage a port -- or rum, as the bar is free (7,6)
I believe the answer is:
harbour master
'i'll manage a port' is the definition.
I can't judge whether this definition defines the answer.
'or rum as the bar is free' is the wordplay.
'is free' is an anagram indicator.
'or'+'rum'+'as'+'the'+'bar'='orrumasthebar'
'orrumasthebar' anagrammed gives 'HARBOUR-MASTER'.
Can you help me to learn more?
(Other definitions for harbour master that I've seen before include "Officer in charge of port" , "Port Authority" , "Official supervising a port" , "Person in charge of anchorage" , "Port supervisor" .)