Pot overturned mostly letting nothing out (3)

I believe the answer is:

tum

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'pot' is the definition.
The answer and definition can be both body parts as well as being singular nouns.
Perhaps there's a link between them I don't understand?

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

Can you help me to learn more?

(Other definitions for tum that I've seen before include "Middle" , "Stomach (informal)" , "Belly" , "Corporation" .)

I've seen this clue in The Times.

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