I have done that before using Pipes, Split and finally Scale1D to flatten things a bit. The results were good, but that just works when the corners are not filleted. Also there is this small edge where the pipes intersect:
I made a plane snapping to the center points of the lower edge of the tile fillets, rebuild the plane with 6x6 points degree 3. Then I selected 4 control points in all corners and elevated it, trimmed off the intersection corners and extruded the remaining edges.
Turn on the control points of the surface in the crossing, then you’ll see…
Thank you. I really like your results, but, too add something to this thread, finally, I figured out, it’s also pretty much like the backside of a classical y branch connection. So that’s also working nicely here.