I personally use a 70% eco-friendly dish soap solution & 30% purified water to clean my outsoles. First wet with a spray bottom, scrub with a brush, and then scrub soap with dish soap dispenser brush until clean. (pictured). Re-spray to remove dirt and grime – then towel or blow-dry (on cold). Always brush with the lines of your shoes respective sole. I also keep a small set of "tools" actually an iPhone tool kit to get hard to reach areas. 

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