A pipe put under water, we hear (4)

I believe the answer is:

duct

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'a pipe' is the definition.
(I've seen this in another clue)

I can't explain the rest of the clue.

(Other definitions for duct that I've seen before include "Pipe, tube" , "Tube for conveing cable, liquid etc" , "Pipe for cables or air" , "Pipe conveying fluid or gas" , "Tube for cables, air, etc" .)

I've seen this clue in The Irish Independent.

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