Drains the French power he’s after (7)

I believe the answer is:

leaches

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'drains' is the definition.
The answer and definition can be both related to change as well as being verbs in their -s form.
Maybe they are linked in a way I don't understand?

'the french power he's after' is the wordplay.
'the french' becomes 'le' ('the' in French).
'power' becomes 'ac' (AC is an example).
'after' says to put letters next to each other.
'le'+'ac'+'hes'='LEACHES'

Can you help me to learn more?

(Other definitions for leaches that I've seen before include "Percolates through soil or ore" , "Bleeds" .)

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

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