Go out back visiting my mate in the outback (6)
I believe the answer is:
cobber
'mate in the outback' is the definition.
(Australian term for friend)
'go out back visiting my' is the wordplay.
'go out' becomes 'ebb' (I've seen this before).
'back' is a reversal indicator.
'visiting' indicates putting letters inside.
'my' becomes 'cor' (both are expressions of surprise).
'ebb' reversed gives 'bbe'.
'bbe' inserted into 'cor' is 'COBBER'.
(Other definitions for cobber that I've seen before include "Mate (Australian)" , "A down-under friend or mate" , "Australian term for a pal" , "Antipodean chum" .)