Don't interfere when pants' seat is missing! (4,3)

I believe the answer is:

butt out

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'don't interfere when pants'' is the definition.
I know nothing about this answer so I cannot judge whether this works.

'seat is missing' is the wordplay.
'seat' becomes 'butt' (synonyms).
'is missing' becomes 'out' (I've seen this in another clue).
'butt'+'out'='BUTT OUT'

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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