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: