Implement for opening this retro dunny (4)

I believe the answer is:

tool

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'implement' is the definition.
(I know that implement can be written as tool)

'opening this retro dunny' is the wordplay.
'opening' says to take the initial letters.
'retro' says the letters should be written backwards (retro is Latin for 'backwards').
'dunny' becomes 'loo' (I can't explain this - if you can you should give a lot more credence to this answer).
The initial letter of 'this' is 't'.
'loo' back-to-front is 'ool'.
't'+'ool'='TOOL'

'for' is the link.

Can you help me to learn more?

(Other definitions for tool that I've seen before include "Device used for work" , "Pawn" , "Implement - agency" , "Hand implement" , "one of 12 [SPADES] , for example" .)

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

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