Soak the leg due to be operated on (6)
I believe the answer is:
deluge
'soak' is the definition.
(thesaurus)
'the leg due to be operated on' is the wordplay.
'to be operated on' indicates an anagram (I've seen this in other clues).
'leg'+'due'='legdue'
'legdue' is an anagram of 'DELUGE'.
(Other definitions for deluge that I've seen before include "Inundation" , "A heavy fall of rain (6)" , "Cloudburst, downpour" , "Torrential rain" , "Overwhelm with water" .)