Such a victory as the road cleaner won over dirt? (8)
I believe the answer is:
'the road cleaner won over dirt?' is the definition.
Both the answer and definition are adjectives. Maybe you can see an association between them that I can't see?
'such a victory as' is the wordplay.
'such a victory' becomes 'sweep' (sweep is a kind of victory).
'as' becomes 'ing' (I can't explain this - if you can you should give a lot more credence to this answer).
Can you help me to learn more?
(Other definitions for sweeping that I've seen before include "not very specific", "Extensive", "Brushing or ignoring distinctions", "Brushing; generalised", "all-encompassing".)