Surface Difference Generates Multiple Outputs

Hello all,

I am having a little trouble with Surface difference. I am try to extract spheres at the corners of my pipe geometry that is surface differenced (boolean difference) with the pipe geometry itself. Instead of getting a single sphere at each corner with multiple pipe extractions I am getting multiple spheres for each pipe extraction. So, for a corner that has 4 pipes meeting at a point with one sphere, I am getting 4 corresponding spheres to each pipe, instead of a single sphere with 4 pipe extractions.

Does anyone know how I can fix this? I have attached my definition. Also I am somewhat new to GH so any critique on my definition would be much appreciated!

Thanks!!