Stop nice man getting cleaner (9)
I believe the answer is:
detergent
'cleaner' is the definition.
(chemical that cleans)
'stop nice man getting' is the wordplay.
'stop' becomes 'deter' (I've seen this in another clue).
'nice man' becomes 'gent' ().
'getting' is a charade indicator (letters next to each other).
'deter'+'gent'='DETERGENT'
(Other definitions for detergent that I've seen before include "cleaner" , "Cleaning product" , "Cleansing substance used for washing clothes" , "help with the washing-up" , "Soluble cleanser" .)