Cleaner emptied out sluice harbouring nasty smell (6)
I believe the answer is:
sponge
'cleaner' is the definition.
'emptied out sluice harbouring nasty smell' is the wordplay.
'emptied out' says to hollow out the word (remove centre letters) (the inside letters are emptied out).
'harbouring' indicates putting letters inside.
'nasty smell' becomes 'pong' (pong can informally mean a bad smell).
'sluice' with its middle taken out is 'se'.
'se' going around 'pong' is 'SPONGE'.
(Other definitions for sponge that I've seen before include "Light cake; aquatic invertebrate" , "drunkard or > hanger-on" , "Light cake; sea creature" , "Marine animal often found in bathroom" , "Marine creature - cadge" .)