Documentary technique not about showing transport (7)
I believe the answer is:
portage
'transport' is the definition.
(thesaurus)
'documentary technique not about' is the wordplay.
'documentary technique' becomes 'reportage'.
'not' is a deletion indicator.
'about' becomes 're' (regarding).
'reportage' with 're' taken out is 'PORTAGE'.
'showing' is the link.
(Other definitions for portage that I've seen before include "Cost of carrying or transporting" , "Carriage" , "Carrying boat overland" , "Transport between waterways" .)