Place the black composite furniture outdoors or in a bathtub and rinse it off with water.
Fill a bucket with hot tap water.
Pour about 1/2 cup of baking soda on a disposable plate.
Dip the scrub brush into the hot water, then press it into the baking soda. Scrub the entire surface of each piece of furniture.
Rinse the baking soda off of the furniture using a bucket of water or a garden hose. Dry with a microfiber cloth or allow it to air dry in the sun.
Mix 1 part of oxygen bleach with 2 parts of hot water to make a paste to clean the furniture if there is extensive sun fading or if any dirt remains on it after scrubbing with baking soda. Rinse and dry.