Cleaner bum (6)

I believe the answer is:

sponge

I believe this clue is a double definition.

'cleaner' is the first definition.

'bum' is the second definition.
('sponge' can be a synonym of 'bum')

(Other definitions for sponge that I've seen before include "Porous mass in oceans" , "marine life?" , "Madeira, say" , "Aquatic invertebrate with a soft porous body" , "Heavy drinker" .)

I've seen this clue in The Guardian.

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