They start as one Closed Brep and one Closed SUbD from the Multi-Pipe command. I am intending to Metal 3D Print the final union so I need a solid / closed object (preferably). Any better ways to union meshes (or Breps and SubDivisions)?
This is impossible to determine the problem. It seems both meshing components are introducing naked edges and non-manifold geometry. So, we would need to look at those objects and take them through a manual meshing command to determine exactly where the mesh goes bad.