Knock back Moray? Time for port docking charge? (7)

I believe the answer is:

keelage

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'port docking charge?' is the definition.
The definition suggests a singular noun which matches the answer.

'knock back moray? time' is the wordplay.
'back' says to take the final letters.
'moray?' becomes 'eel' (moray is a kind of eel).
'time' becomes 'age' (an age is a period of time).
The final letter of 'knock' is 'k'.
'k'+'eel'+'age'='KEELAGE'

'for' is the link.

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

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