Old chore, having left tax (6,4)

I believe the answer is:

export duty

'tax' is the definition.
(I know that export duty is a type of duty)

'old chore having left' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'chore' becomes 'duty' (I've seen this in another clue).
'having' indicates putting letters inside.
'left' becomes 'port' (left side of a ship - opposite of starboard).
'ex'+'duty'='exduty'
'exduty' enclosing 'port' is 'EXPORT DUTY'.

I've seen this clue in The Daily Express.

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