ISO 23309:2007

ISO 23309:2007 specifies the procedures for flushing from the hydraulic lines of larger hydraulic fluid power systems solid particulate contamination that can be introduced during the initial build of a new hydraulic system or after maintenance or modification of an existing system.
ISO 23309:2007 supplements, but does not replace, the requirements of the component supplier and customer, especially when those requirements are stricter than those specified by this International Standard.