In a wastewater treatment plant a rag seeding tank is included in a process drain to collect hair and fibers which have passed through headworks of the plant. The hair and fibers tend to join together into large masses downstream of the headworks and can be damaging to process zones, particularly membrane zones. The rag seeding tank includes cartridges filled with surfaces that fibers and hair will attach to, so that hair/fiber rags grow in the seeding tank and are removed therefrom rather than causing problems downstream.