Remove the prefilter and shake out or brush off the accumulated dust and lint. If this is not adequate, a vacuum cleaner may be used or the prefilter can be cleaned with an all-purpose alkaline detergent to remove tobacco smoke and cooking grease stains. A thorough rinsing is required after each cleaning. The pre-filter should be completely dried before inserting back into the unit. The pre-filter will need to be replaced after several washings as the the material will naturally begin to deteriorate.