Made use of, as graffiti-covered wall has been (5,2)

I believe the answer is:

drawn on

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'made use of' is the definition.
(drawing on is a kind of making use of)

I cannot understand how the rest of the clue works.

(Other definitions for drawn on that I've seen before include "used" , "Sketch pad may be" .)

I've seen this clue in The Times.

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