Cleans up after many operations (4)
I believe the answer is:
mops
'cleans up' is the definition.
(I've seen this in another clue)
'after many operations' is the wordplay.
'after' says to put letters next to each other.
'many' becomes 'm' (Roman numeral for a thousand).
'operations' becomes 'ops' (abbreviation).
'm' put next to 'ops' is 'MOPS'.
(Other definitions for mops that I've seen before include "They're used to clean floors" , "grimaces" , "Swabs, wipes up" .)