Pretty good cleaner will leave things thus (3,2,5)
I believe the answer is:
not so dusty
'pretty good' is the definition.
'cleaner will leave things thus' is the wordplay.
I cannot quite see how this works, but
'thus' could be 'so' (synonyms) and 'so' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for not so dusty that I've seen before include "Fairly well" , "when the daily's been" , "Reasonably good" , "Quite good (after housework?)" , "It's fairly good" .)