K&N part 99-0621 is a 32 ounce pump spray bottle of Power Kleen Air Filter Cleaner. K&N Power Kleen is the only cleaner recommended to clean K&N cotton air filter elements. K&N 99-0621 Air Filter Cleaner will loosen and remove built up dirt and grime from your K&N oiled cotton air filter so it can be washed clean with water. It is so good at cleaning greasy dirt and grime that it is also used as an industrial strength degreaser. After your K&N air filter dries re-oil it with K&N air filter oil (sold separately). How Do I Clean My K&N Air Filter Once you determine your K&N air filter needs to be cleaned, K&N air filter cleaning kits simplify the process and restore your air filter to a like new condition. Cleaning your K&N air filter is simple when following the 4 easy steps below. STEP 1 - APPLY K&N AIR FILTER CLEANER Liberally spray K&N Air Filter Cleaner onto both sides of filter and allow to soak for 10 minutes to loosen the dirt. Do not allow cleaner to dry on air filter. STEP 2 - RINSE YOUR K&N AIR FILTER Rinse off your air filter with cool low-pressure water applied to the clean side out in order to flush the dirt out of the filter. Continue to rinse the filter until all traces of cleaner are gone. It may be necessary to repeat steps 1 and 2. STEP 3 - DRY YOUR K&N AIR FILTER After rinsing your filter, gently shake off the excess water and only allow filter to dry naturally. Do not apply oil until the air filter is completely dry. STEP 4 - APPLY K&N FILTER OIL When using the air filter oil squeeze bottle found in K&N filter cleaning kit 99-5050, apply K&N air filter oil evenly along the crown of each pleat. Allow the oil to wick for approximately 20 minutes then touch up any light areas on either side of filter until there is a uniform red color at all areas. K&N offers 1/2 ounce pillow pack air filter oil for the smaller jobs and one gallon jug air filter oil for bigger jobs. Individuals who require a large supply of oil on hand, K&N also offers 5 gallon pails of air filter oil.