You talking about the foam outer part? Use some 409 or a similiar type of cleaner. Just spray it on, let it sit for a minute or two and hose it off. Or use Dawn dishwashing soap. Mix some in some warm water, let it soak for a while then rinse it out with warm water. Either way blow out the moisture with an air hose or let it air dry then reapply the "oil spray" that came with it.