Waxed canvas should never be dry cleaned or machine washed. It can be cleaned carefully by hand. Brush off the loose dirt, rinse the surface with cold water, gently scrub with a brush, then let air dry. If stains persist, use mild bar soap or saddle soap.
After cleaning, waxed canvas may need to be re-waxed. To do so, use a wax conditioner and apply following the manufacturer's instructions.