Refuse sleep when crossing river (5)
I believe the answer is:
dross
'refuse' is the definition.
(both can mean rubbish)
'sleep when crossing river' is the wordplay.
'sleep' becomes 'doss' (I've seen this in other clues).
'when crossing' indicates putting letters inside.
'river' becomes 'r' (abbreviation for river).
'doss' going around 'r' is 'DROSS'.
(Other definitions for dross that I've seen before include "Waste coal - rubbish" , "Worthless matter" , "Scum on molten metal" , "Rubbish; impurities" , "Refuse - dregs" .)