Government department uncovered waste product (4)
I believe the answer is:
urea
'waste product' is the definition.
(I've seen this before)
'government department uncovered' is the wordplay.
'government department' becomes 'bureau' (I've seen this before).
'uncovered' means to look at the middle letters.
The central letters of 'bureau' are 'UREA'.
(Other definitions for urea that I've seen before include "Compound found in urine, synthesised as a fertiliser" , "It's produced by piddling" , "organic compound" , "Waste matter" , "Human waste product" .)