It's hard work sorting waste (5)

I believe the answer is:

sweat

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'it's hard work' is the definition.
(synonyms)

'sorting waste' is the wordplay.
'waste' can be anagrammed to 'SWEAT'.
But, I am not clear how this is indicated.

Can you help me to learn more?

(Other definitions for sweat that I've seen before include "It's hard work" , "Salty fluid secreted by the body" , "(Of argument) intense" , "Male perspiration?" , "Soldier" .)

I've seen this clue in The Globe and Mail.

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