Replaces spittoon containing pool of foul liquid (7)

I believe the answer is:

cesspit

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'pool of foul liquid' is the definition.
'cesspit' can be an answer for 'pool' (cesspit is a kind of pool). I am unsure of the 'of foul liquid' bit.

'replaces spittoon containing' is the wordplay.
'containing' says the answer is hidden in the clue.
'CESSPIT' is hidden within 'replaces spittoon'.

Can you help me to learn more?

(Other definitions for cesspit that I've seen before include "Sewage storer" , "Sewage receptacle" , "Sewage holder" , "Foul and squalid place" , "Place for filthy water" .)

I've seen this clue in The Guardian.

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