Writer touched rubbish pile by pigsty (4-3,3)

I believe the answer is:

felt-tip pen

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'writer' is the definition.
(I've seen this before)

'touched rubbish pile by pigsty' is the wordplay.
'touched rubbish pile' becomes 'felttip' (I can't explain this - if you can you should give a lot more credence to this answer).
'by' means one lot of letters go next to another.
'pigsty' becomes 'pen' (I've seen this in another clue).
'felttip'+'pen'='FELT-TIP PEN'

Can you help me to learn more?

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

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