Make sure there's no vacancy at the petrol station (4,2)

I believe the answer is:

fill up

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'make' is the definition.
(thesaurus)

I don't understand how the remainder of the clue works.

(Other definitions for fill up that I've seen before include "Put petrol in car" , "Occupy (some time)" .)

I've seen this clue in the Evening Standard.

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