One of the best ways to keep your indoor outdoor fabrics looking good is to properly maintain the fabrics. This can be accomplished by simply brushing off dirt before it becomes embedded in the fabrics, wiping up spills as soon as they occur or spot cleaning soon after. For removable cushion covers and slipcovers:
Soak fabric in a solution of 70mls of mild liquid soap such as Dawn dishwashing detergent per 4l of lukewarm water.
Use a sponge or a soft bristle brush as necessary.
Rinse thoroughly to remove all soap residue.
Machine wash in cold water with mild laundry soap.