Fluid transfer interfaces for transferring fluid into or out of vessels, namely flexible polymeric bags. The fluid transfer interfaces have a body for use in connection with a vessel, or combined therewith, one or more apertures extending through the body, and one or more fluid transfer conduits secured to the body by way of a cast seal and extending continuously and axially through the one or more apertures. Also disclosed is a vessel closure having one or more fluid transfer conduits extending through the closure, the fluid transfer conduits affixed to the closure by a cast seal.