From the Manufacturer: Sunbrella ®

     Sunbrella® fabric should be cleaned regularly before substances such as dirt, mold, mildew, etc. are allowed to accumulate on and become embedded in the fabric. The fabric can be cleaned without being removed from the installation.  Simply brush off any loose dirt, hose down and clean with a mild solution of natural soap in lukewarm water (no more than 100º F).  Rinse thoroughly to remove soap.  DO NOT USE DETERGENTS.   Allow to air dry!

    TIP: Use "Spray-n-Wash ®" to remove stubborn bird droppings and seagull residue (It won't hurt the fabric.)

    For more stubborn cases:  Soak the fabric for approximately twenty minutes in a solution of no more than 1/2 cup of a non-chlorine bleach and 1/4 cup natural soap per gallon of water at approximate 100º F.  Rinse thoroughly in cold water to remove all of the soap.  Note:  excessive soaking in non-chlorine bleach can deteriorate sewing threads.  This method of cleaning may remove part of the water repellency and the fabric should receive an application of an air-curing fluorocarbon water repellent treatment, if water repellency is a factor.  

If you are cleaning Sunbrella® while still on a frame or on a boat, follow these simple steps:

Brush off loose dirt.

Hose it down.

Prepare a cleaning mixture of water and mild, natural soap (no detergents).

Use a soft bristle brush to clean.

Allow soap to soak in.

Rinse thoroughly.

Air dry.

If stubborn stains persist, you can use a diluted chlorine bleach/soap mixture for spot cleaning of mildew, roof run-off and other similar stains.

Prepare a special cleaning mixture:

Four ounces (half cup) of chlorine bleach.

Two ounces (one-fourth cup) of natural soap.

One gallon of water.

Clean with soft bristle brush.

Allow mixture to soak for up to 20 minutes.

Rinse thoroughly.

Air dry.

Repeat if necessary.