Knowing generous patron, his crime is a load of rubbish (3-6)
I believe the answer is:
fly-tipper
'his crime is a load of rubbish' is the definition.
(a fly-tipper dumps rubbish)
'knowing generous patron' is the wordplay.
'knowing' becomes 'fly'.
'generous patron' becomes 'tipper' (someone who gives tips).
'fly'+'tipper'='FLY-TIPPER'
(Other definitions for fly-tipper that I've seen before include "Illegal rubbish dumper" , "Person dumping rubbish illegally" .)