Crapulent royal fed a long drink? (4,2,3)

I believe the answer is:

yard of ale

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

'long drink?' is the definition.
(I've seen this before)

'crapulent royal fed a' is the wordplay.
'royal fed a' anagrams to 'YARD OF ALE'.
But, I am not clear how this is indicated.

Can you help me to learn more?

(Other definitions for yard of ale that I've seen before include "Long drink" , "Narrow glass" , "Tall glass" , "Glass of beer" , "Element in beer contest" .)

I've seen this clue in The Independent.

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