Methods and devices are disclosed herein that generally involve a sterile catheter-dressing system that allows for integrated injection of fluids, e.g., a saline flush, during the process of catheter insertion and sterile dressing placement. Such methods and devices can be used as a fully integrated catheter insertion system, or to convert existing catheter insertion devices and methods into integrated flush and sterile sealing catheter-dressing systems. Such methods and devices can greatly simplify the catheter insertion process, and can allow the reproducible placement of a fully sterile and flushed vascular catheter, as well as the placement of a durably sterile circumferentially sealing and securing dressing.