Drink downstairs? Nonsense, according to a shanty singer (8)

I believe the answer is:

rumbelow

'nonsense according to a shanty singer' is the definition.
(nonsense word in sea shanties)

'drink downstairs?' is the wordplay.
'drink' becomes 'rum' (rum is a kind of drink).
'downstairs?' becomes 'below' ('below' can be a synonym of 'downstairs').
'rum'+'below'='RUMBELOW'

I've seen this clue in The Guardian.

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