Measure depth then fit the pipes (5)

I believe the answer is:

plumb

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'measure depth' is the definition.
(I've seen this in another clue)

I can't explain the remainder of the clue.

(Other definitions for plumb that I've seen before include "Connect pipes" , "Exactly - perpendicular" , "Weight to show vertical direction" , "For Americans, quite" , "Fathom - out-and-out" .)

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

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