Oh my goodness, that is nuts!! Did the dr tell you that or one of the RT's? I'd print off some info that is published by the CFF itself and bring it to clinic to back up the need for sterilizing equipment.
When Emily was admitted the RT's were specifically instructed to provide fresh neb cups every single time Emily did vest/nebs- so obviously our team believes a fresh, sterile neb is vital every. single. time. ...they back up their instructions to us with action when the kids are in the hospital!