3D Printing Model Correction Here's a relatively simple model that I want to print (for bathtub drain). It is made by only creating cylinders and cubes and applying Array and Boolean modifiers.



When I import it as .stl and load it to Slic3r (for correct result, scaling by 100000% should be used since .stl doesn't contain the scale), it shows this in 3D:



which is ok, but there's warning which sais "Auto-repaired (18 errors)" and tooltip sais that "5 degenerate facets, 5 facets removed, 4 facets added, 4 facets reversed" and Preview shows this:



and Layers shows this for the first layer:



I wonder what I'm doing wrong and how to fix this. I haven't tried to print this yet, but the preview suggests that it will be no good. Here's the .blender file: .
Perhaps Multiple Problems.
Edit Mode.  Select Non-Manifold identifies some problems. 
See Arrow in image above.
Add faces to holes you see.



Strange face. Edit Mode Face Selection. See arrow. Remove doubles can correct partially. Image above. 

Look for more problems.  This does not strive to be a tutorial.

Consider using Blender Mesh [Join]. Inspect each time with the menu choices of the first image.

Consider converting all n-gons to quadrangles or triangles. Quads and Tris.

Consider the Remesh Modifier. There is an Apply button.

Consider duplicating the mesh and making corrections to improve to the point when your 3D printer software has zero warnings.  I do not have your 3D printing software.