The poultry plumbers know about? (5)

I believe the answer is:

cocks

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

'the poultry' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for cocks that I've seen before include "Raises" , "Roosters" , "poultry" , "Male birds" , "Adult male chickens" .)

I've seen this clue in the Evening Standard.

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