Just started 3d printing a couple months ago. I'm having trouble when I print part of my model. This particular part is supposed to be hollow, but S3D is adding infill and a couple of walls. Most of the problems that I read about address the issue of S3D leaving holes where there are not supposed to be. I'm trying to do the opposite - create holes where they are intended to be. I have attached a few different views. One shows the solid model, which shows that there is supposed to be a hole. The others show various views, including color-coded layers when I generate the preview. In this view, you can see the infill and other extrusions. Another view shows red color, indicating non-manifold edge (if I understand the term properly). How do I repair so that the red color is actually a wall with everything inside of it being empty? I would appreciate any guidance.