Scum; rubbish (5)
I believe the answer is:
dross
This clue is a double definition.
'scum' is the first definition.
(I know that dross is a type of scum)
'rubbish' is the second definition.
(I've seen this before)
(Other definitions for dross that I've seen before include "Waste coal - rubbish" , "It's Poor" , "Scum - dregs" , "Scum on molten metal" , "of no value" .)