Amounts of paper are wasted on manuscript (5)
I believe the answer is:
reams
'amounts of paper' is the definition.
(I've seen this in another clue)
'are wasted on manuscript' is the wordplay.
'wasted' is an anagram indicator.
'on' means one lot of letters go next to another.
'manuscript' becomes 'ms' (abbreviation for manuscript).
'are' anagrammed gives 'rea'.
'rea'+'ms'='REAMS'
(Other definitions for reams that I've seen before include "Large quantities (of paper?)" , "a very large amount" , "Large quantity of written matter" , "Scrapes the barrel" , "Lots of paper" .)