Set the mud- and clay-stained boots on top of a layer of newspaper. Allow the mud to dry completely.
Pry and scrape chunks of dried mud off the surface of your boots with a plastic scraper. Insert the edge of the scraper underneath the mud and pry to loosen it. Continue to chip, pry and scrape to remove as much of the dried mud and clay as possible.
Brush dried mud dust and particles off the surface of the boots with a nonmetallic scrub brush. Use a vacuum with upholstery attachment to remove mud and clay dust.
Pour 2 cups of warm water into a bucket. Add 1 teaspoon of dishwashing detergent.
Soak a sponge in the diluted detergent solution. Squeeze the sponge to remove excess moisture.
Wipe off remaining mud and clay stains from the surface of your boots. Rinse the sponge frequently. Apply more detergent mixture and continue to wipe and sponge the boots to remove the mud and clay completely.
Wet a clean cloth with water. Wring out the cloth. Blot the surface of your boots to rinse them. Press a dry cloth into the surface to remove excess moisture.
Fill your boots with newspaper to hold the shape as they dry. Place them in a location away from heat and direct sunlight. Allow your boots to air-dry completely.