Waste, speaking when wasted? (6)

I believe the answer is:

slurry

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'waste' is the definition.
(I have seen 'Liquid waste ' mean 'slurry' so perhaps 'waste' could also mean 'slurry')

I don't understand how the rest of the clue works.

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(Other definitions for slurry that I've seen before include "Liquid manure as fertiliser" , "Semi-liquid mixture containing manure, cement or coal, for example" , "Water mixed with clay, lime etc" , "Semi-liquid mixture of water and cement or manure, say" , "Liquid waste from farm animals" .)

I've seen this clue in The Guardian.

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