Maybe Dave but I am still not sure if I understand either. I thought the same thing when I read the "2unit pipe" bit. But, his response to your post has me more confused. It seems he is describing something more then just the boolean difference. I guess we will know when he watches the video.

It seems to me that boolean difference is pretty straight forward. However, I did not mention that if the surface normals of the two parts are not in the same direction then the booleans will not behvae as expected. So maybe that is what is happening.