If you just want to get most of the dust and dirt out, its almost easier to just fill up a big bucket (and i mean like big, a rubbermaid container works well, or one of those 'industrial size' laundry baskets) and wash it by hand. I dont mean by hand by hand, but mix in some detergent and use a mild brush on problem spots and clean it that way. Only problem with that is you have to be sure to rinse it out really well. I usually wash mine in the spring right after winter, and then again right after summer. It stays pretty clean, but it cant hurt to clean it.