Assemblies and methods of inserting a delivery system assembly into a working channel are disclosed. In accordance with some embodiments, a sealing insert is configured to reduce fluid leakage and spray-back. In accordance with some embodiments, a sealing insert is disclosed in which a distal sealing surface is configured to seal against differently sized working channels of a plurality of endoscopes. In accordance with some embodiments, a sealing insert is disclosed in which a cap is configured to control a seal between a sealant and a delivery system assembly.
