Crossword Genius

Wrap up piece of plumbing emerging from bathroom? (4,4)

Ross

I believe the answer is:

pipe down

I'm a little stuck... Click here to teach me more about this clue!

'wrap' is the definition.
Although both the answer and definition are verbs in their base form, I don't understand how they can define each other.

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for pipe down that I've seen before include "make less noise" , "Sh!" , "Shut up!" , "Stop talking" , "Be quiet!" .)

I've seen this clue in The Telegraph.
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