Where soil is of a stubborn nature, (as frequently found in industrial areas) the following cleaning solution works well:
1/3 cup (80 ml) laundry detergent
2/3 cup (160 ml) of trisodium phosphate
1 gallon (4.5 liters) of water
In certain geographical areas where mildew may be a problem, substitute one quart (one liter) of 5% sodium hypochlorite (household bleach) for one quart (one liter) of water in the above formula.
When stubborn stains must be removed from a panel, an abrasive-type cleaner, may be used without damage to the siding. The most damage that can be done to a panel of vinyl siding is to scratch or roughen the surface. This, however, is rarely visible a few feet from the house.
Where the house is extremely dirty, it is recommended that you start washing from the bottom and go to the, top, rinsing frequently. Cleaning solutions should be permitted to stand on the surface of the siding for several minutes before rinsing.
When using any cleaning agents, be sure to observe the precautionary labeling instructions on the cleaning agent container and protect shrubs and plants from direct contact with cleaning agents.