Remove impurities from cloak, regularly dipped in river (6)

I believe the answer is:

decoke

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'remove impurities' is the definition.
'decoke' can be an answer for 'remove' (decoking is a kind of removing). I am not certain of the 'impurities' bit.

'cloak regularly dipped in river' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'dipped in' indicates putting letters inside.
'river' becomes 'Dee' (River Dee).
The alternating letters of 'cloak' are 'cok'.
'cok' placed inside 'dee' is 'DECOKE'.

'from' is the link.

Can you help me to learn more?

(Another definition for decoke that I've seen is " Remove built-up carbon from an engine".)

I've seen this clue in The Times.

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