One option is to keep the fabric on the frame, scrub it with a mild soap/detergent, and hose it off. You can also remove the fabric and submerge it in a tub full of water with mild detergent. In both cases, let the fabric air dry for 24-48 hours. Avoid putting it in a washing machine, as the spin cycle and agitator can break the buckles. Drying in a tumble dryer is also not recommended.