Fill the hose end sprayer with 1 gallon of hot water and 3 cups of regular mild dish soap. Attach the sprayer to the hose by screwing it on. Flip the sprayer to the hose mist or light spray setting. The exact name of the setting may vary.
Spray the painted cedar siding with water only. Use a mist or light spray because a strong spray can chip the paint. Remove the excess and loose grime and filth from the siding.
Switch the nozzle to the cleaning mixture. Mist the cedar siding using a back-and-forth motion. Soak the entire area before letting it sit for roughly 12 minutes.
Scrub the siding with a long-handled squeegee. Avoid using a bristle brush as this can scratch the painted surface. Scrub upward, starting at the bottom of the cedar siding. This prevents dirt from streaking downward on the siding. Remove as much filth as possible before continuing.
Turn the hose end sprayer back to the light hose spray setting. Clean the soap and remaining grime off the siding. Stand roughly 4 feet away from the cedar while washing. Hold the hose in one spot for about 20 seconds before moving on to another part of the siding.