How one gets the dirt on one's shoes! (5)

I believe the answer is:

pumps

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'shoes' is the definition.
(pump is a kind of shoe)

I don't understand the rest of the clue.

(Other definitions for pumps that I've seen before include "needed by cyclists" , "Forces liquid to move; light shoes" , "Mechanical devices that move fluid or gas" , "Light dancing shoes - force air into" , "Plimsolls" .)

I've seen this clue in the Evening Standard.

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