Take in water when the plug is out (4)

I believe the answer is:

gulp

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'take in' is the definition.
(gulping is a kind of taking in)

'water when the plug is out' is the wordplay.
'plug' anagrams to 'GULP'.
But, I am not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for gulp that I've seen before include "Noise made when swallowing too quickly" , "Swallow audibly" , "Swallow hurriedly" , "Swallow quickly" , "Audible swallow" .)

I've seen this clue in The Irish Independent.

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