Imposing American can painter (8,4)
I believe the answer is:
augustus john
'painter' is the definition.
'imposing american can' is the wordplay.
'imposing' becomes 'august' (I've seen this before).
'american' becomes 'us'.
'can' becomes 'john' (slang for toilet).
'august'+'us'+'john'='AUGUSTUS JOHN'
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