For extra convenience and servicing ability choose the Pro Dry S material. There is no need for oil and therefore maintenance is a snap. Two layers of randomly porous material ensure that 99.2% of all debris get caught and not swallowed. To clean the material all you must do is shake it and spray it out with an air compressor. The Pro Dry S media is a lifetime filter. All you need to do is pull it out, blow it off, and stick it back in!