New (unwanted) Surfaces in Shapeways Rendering of My .stl File

I have created a model which depicts a velocity stack to be attached to a motorcycle carburetor. The design as it appears on in SketchUp and Mesh Lab is a flared tube, open at both ends. When I upload the file to Shapeways, the model has two new surfaces that close off the tube at both ends. This is first and foremost completely counter productive to the function of what I am trying to create, but also creates the object to be completely solid and much more expensive for production. I would truly appreciate any advice on how to correct this issue if there is something I can do on my end. Otherwise, if Shapeways could look into the case for me, that would be awesome too.

I would prefer to not have to carve these out of wood.

Thanks,

Grant

Both ends of the flare have "collars" that you added, but those extra parts didn't get merged into the main body correctly.

I don't know how to fix it in Sketchup (check other forum posts), but I was able to repair it in Truespace.

Note: I had to magnify the item by 25.4 to be able to work on it properly. If you initially uploaded in inches, you'll need to upload this one as millimeters.

Thanks a lot,
I am working on opening the file right now to see what changes were made. Unfortunately, SketchUp does not support the .stl file type, so I am stuck having to route it through MeshLab to convert the file. MeshLab however does not run well on a Mac and keeps crashing. When I get there I will be studying what you have done closely and trying to learn from my mistake.

Thanks again,

Grant