The most common and most likely answer to this crossword clue is the 9 letter word EFFLUENTS
I've seen this crossword clue in The Guardian
E
F
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L
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Buddy explains!
The straight part
We know that "waste/waste" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case waste/waste = effluents.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does EFFLUENTS mean?
EFFLUENTS noun- A stream that flows out, such as from a lake or reservoir; an outflow; effluence.
- Sewage water that has been (partially) treated, and is released into a natural body of water; a flow of any liquid waste.