Wipe with Paper Towel: Place your fresh mushrooms on a dry, clean surface, and wipe the caps and stems off with a damp paper towel. If you want to reduce time, you can use a sharp knife to remove the stems.
Rinse in Colander: Place a colander in your kitchen sink and turn on cool running water. Place mushrooms in the colander, and use your hand to move water all over the mushrooms. Allow the mushrooms to dry thoroughly before using.
Wash in Bowl: Fill a large bowl with cold water and place a clean towel nearby. Add a handful of mushrooms in water at a time, doing this in batches. Swirl the mushrooms around for a short soak--less than 10 seconds and immediately remove them to the towel nearby. Pat them dry and lay them mushroom cap up. Use a very damp paper towel to remove any excess dirt and allow the mushrooms to dry thoroughly before cooking.