So a gin is mixed with old port (6)
I believe the answer is:
saigon
'old port' is the definition.
The definition and answer can be both locations as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'so a gin is mixed' is the wordplay.
'is mixed' is an anagram indicator.
'so'+'a'+'gin'='soagin'
'soagin' is an anagram of 'SAIGON'.
'with' acts as a link.
Can you help me to learn more?
(Other definitions for saigon that I've seen before include "city in Asia" , "Musical set in Vietnam war - ''Miss . . . . . .''" , "Former name of Ho Chi Minh City" , "See 8" , "Asian city once" .)