Attach pipe lacking diameter to draw inward (6)

I believe the answer is:

adduct

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'draw inward' is the definition.
'adduct' can be an answer for 'draw' (adducting is a kind of drawing). I am not sure about the 'inward' bit.

I don't understand the rest of the clue.

Can you help me to learn more?

(Another definition for adduct that I've seen is " Draw in".)

I've seen this clue in The Sunday Times and The Times.

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