Cleaner removing outside smell (4)
I believe the answer is:
pong
'smell' is the definition.
(pong can informally mean a bad smell)
'cleaner removing outside' is the wordplay.
'cleaner' becomes 'sponge'.
'removing outside' says to take the centre.
The middle letters of 'sponge' are 'PONG'.
(Other definitions for pong that I've seen before include "In slang, a real stink" , "It may make one wrinkle nose" , "Smell unpleasantly" , "Horrid smell (informal)" , "Bad smell" .)