Dyson Vacuum Filters: Dyson 911685-01 DC18 Slim Motor Filter. Aftermarket Replacement. This filter is a washable replacement for the lifetime filter 911685-01 in your vacuum. Depending on your needs the filter needs to be washed at least one time within a 3 to 6 month period. Also allow the filter to dry completely, usually overnight, before putting it back into service. Failure to allow the filter to dry completely may cause damage to your machine. It is suggested to have 2 filters, 1 in the machine while the other dries out. This could save you money in the long term by not damaging your machine. The number 911685-01 is for reference only. This is an aftermarket filter.