First, choose a warm, sunny day for this task, combine warm water and mild dish soap in a bucket. Remove any cushions, tablecloths or other decorative items from your poly furniture. Dip a clean rag into the water-and-soap solution. Then, gently scrub the surface of your poly furniture, paying careful attention to any grooves in the material where dirt could get caught. Once you’ve finished scrubbing, rinse the furniture with clean water from your hose and allow to air dry.