Scrap outhouse around river (5)
I believe the answer is:
shred
'scrap' is the definition.
(both can mean a small amount of material)
'outhouse around river' is the wordplay.
'outhouse' becomes 'shed' (a shed is an outside building).
'around' means one lot of letters goes inside another.
'river' becomes 'r' (abbreviation for river).
'shed' placed around 'r' is 'SHRED'.
(Other definitions for shred that I've seen before include "Strip of material; a very small amount" , "(Reduce to) small piece(s)" , "Tiny amount" , "Small piece torn from something" , "Torn piece of material" .)