Begin by using a shovel or other flat-edge tool to loosen and remove the large chunks of dirt and debris from the screen. You can then use a garden hose to rinse the screen thoroughly and remove smaller pieces of dirt that could not be easily scooped or scraped off. Once the screen is clean of all debris, use clean tap water and a cloth to gently wash the screen, being sure to remove all dirt and dirt particles from the screen completely. Rinse again with the hose to ensure all of the soap and debris are washed away. Finally, use a soft dry cloth to buff the screen dry.