Slic3r doesn't handle hole in box interior

I'm working on a box with a 12 mm deep bottom with 15 mm holes 10 mm deep in it. Slic3r consistently creates G code that ignores the holes. KIsSlicer handles it just fine.
Slic3r also complains about the model being non-manifold but Blender reports that the model IS manifold.
Anyone seen this before?
BTW I am a long-time C/C++ programmer and would be glad to help out. I use Embarcadero RAD Studio and a variety of open source tools.

Try running it through cloud.netfabb.com to see if that fixes it - I often find that if slic3r complains about an stl being non-manifold then it will have problems slicing correctly. I suspect that the file is broken, but I don't know why blender thinks it's ok.

Thanks. I'll try that and get back to you on the result. I would be glad to post the file.

Thanks for the tip about the cloud.netfabb.org. I submitted the file to them and they fixed it! Now Slic3r handles it just fine.
I did notice that the triangle count went from about 6,000 to 16,000. I'll open the file up in Blender again to see what changes were made.

Reef

Cool glad you got it sorted. There's a useful python script to automate the process instead of using a web form: [www.dropbox.com]

Reef, the poor STL format sometimes causes loss of manifoldness at export time, even if your original mesh is correct. You can try exporting in OBJ format. I recommend to download the free Netfabb Studio Basic to quickly check whether a given STL file is valid or not. You can use that to double-check the Slic3r warnings if you suspect it's not telling the truth.

Thanks, The feedfack STL_fixed. work nice!