Remove piping that's not straight (7)

I believe the answer is:

unplumb

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'remove piping' is the definition.
The definition suggests an adjective which matches the answer.

'not straight' is the wordplay.
'not' becomes 'un' (prefix meaning 'not').
'straight' becomes 'plumb' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'un'+'plumb'='UNPLUMB'

'that's' acts as a link.

Can you help me to learn more?

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

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