Sweat is such a product (5)
I believe the answer is:
waste
'a product' is the definition.
The answer and definition can be both substances as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'sweat is' is the wordplay.
'sweat' can be anagrammed to 'WASTE'.
Though, I'm not sure how this is indicated.
'such' acts as a link.
Can you help me to learn more?
(Other definitions for waste that I've seen before include "Fail to use (profitably)" , "Become gradually weaker" , "unused" , "Misuse" , "Barren area; rubbish" .)