well there's many ways of doing this, but I will share only the fast and most flexible method.
Create one tube, then on the center project a cirkle using Itoosoft free plugin "Glue" and once projected unto the middle part of the tube, then extrude out, and then do same thing for the other side of the tube. Once finished, attach all meshes together and then weld all vertices. Make sure
you work with same type of vertices, so everthting aligns perfectly.
After welding all vertices you could do more flanging and roundness at the intersection areas.