Nothing is cleaner! (6)
I believe the answer is:
vacuum
This clue is a double definition.
'nothing' is the first definition.
(thesaurus)
'is cleaner' is the second definition.
(I've seen this before)
(Other definitions for vacuum that I've seen before include "Nature abhors one" , "Entirely empty space" , "Space containing no matter" , "Area containing no matter" , "Absence of matter" .)