Use a mop (4)
I believe the answer is:
swab
'use a mop' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for swab that I've seen before include "Absorbent surgical pad" , "Small piece of cotton used to cleanse a wound" , "Hospital cleaner" , "Pad used in surgery" , "Wound-cleaner" .)