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Disinfects portals after hesitation, if going back round (9)

Ross

I believe the answer is:

fumigates

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'disinfects' is the definition.
Although both the answer and definition are verbs in their -s form, I can't understand how they can define each other.

'portals after hesitation if going back round' is the wordplay.
'portals' becomes 'gates' (I've seen this in another clue).
'after' says to put letters next to each other.
'hesitation' becomes 'um' (um is said in hesitation).
'going back' says the letters should be written backwards.
'round' means one lot of letters goes inside another.
'if' backwards is 'fi'.
'um' inserted inside 'fi' is 'fumi'.
'gates' put after 'fumi' is 'FUMIGATES'.

Can you help me to learn more?

I've seen this clue in The Daily Express.
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