Drunken party-pooper flat out (4,4)

I believe the answer is:

full bore

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

'flat out' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'drunken party-pooper' is the wordplay.
'drunken' becomes 'full' (I can't justify this - if you can you should believe this answer much more).
'party pooper' becomes 'bore' (I've seen this in another clue).
'full'+'bore'='FULL-BORE'

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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