That 3 parts water to 1 part bleach sounds a little strong. For vinyl siding on a home, people usally recommend 1 part bleach, to 9 parts water. Brush on mixture/lightly scub affected area with a nylon bristle brush (keep it off the metal surfaces as much as possible), wait 10 minutes, and hose the whole area off with PLENTY of water. Repeat if necessary. Keep in mind that 3 - 6% sodium hypochlorite (common store bought bleach) corroides the shit out of exposed metal.