Ship's wastewater (5)
I believe the answer is:
bilge
'ship's wastewater' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for bilge that I've seen before include "Hogwash" , "Rubbish - water in boat" , "Rubbish, nonsense; dirty water in ship" , "Piffle - part of hull" , "(Water at) bottom of ship" .)