Many air purifiers use non-washable HEPA filters. Turn off and unplug your appliance before accessing the filter. Check your product manual for specific instructions on how to access your appliance's filter. At least one foam or activated charcoal filter usually accompanies a non-washable HEPA filter. These accompanying filters typically need to be rinsed for two to three minutes, or until water runs clear. Towel dry your foam or activated charcoal filters, then let them air dry completely for at least 24 hours. Use your vacuum cleaner's hose with a nozzle or brush attachment to clean your non-washable HEPA filter. Run the attachment over the filter until you've removed all debris. Take care not to puncture the filter with the vacuum attachment. Reassemble your appliance after the washable filters have dried. You can wrap the HEPA filter tightly in plastic while you're waiting for the other filters to dry or during any other extended period of non-use. Some air purifiers have an electronic filter clean reminder. If yours has one, reset it after cleaning your filter.

Summary:
Remove the filter from your appliance. Wash your appliance's other filters. Run a vacuum cleaner hose attachment over the filter. Reassemble the appliance.