Ssiri

Here's the file I'm using. Bong Beaker.stl

I'm trynna print a bong so obviously it has to be hollow but whenever I import it into cura it says it's not manifold and highlights the open spot on the mouthpiece and inside wherever there's an edge. If I go into blender and press the "make manifold" button it just fills in all the holes but I need it to be hollow so it will function correctly. I don't want to try to print it and risk wasting material just for it to print incorrectly and I can't find anybody online with the same problem. When I slice it and watch the preview it fills in wherever I extruded because there's a missing face but I need there to be no face so it's hollow.