Nut vessel? (3)

I believe the answer is:

tun

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'vessel?' is the definition.
(type of vessel for beer)

'nut' is the wordplay.
'nut' anagrams to 'TUN'.
But, I am not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for tun that I've seen before include "vessel" , "Nut found in large cask" , "'Large cask, for beer perhaps (3)'" , "Cask, vat" , "Large cask (holding 252 gallons)" .)

I've seen this clue in the Evening Standard.

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