Making a Y tube (manifold)

Start by using the line command and arc command to draw the path of one half of the Y
The draw a circle at the end of the path the size of the final pipe
Use Follow me to create the volume of the pipe (circle along the path)
Select all (I inverted faces) and use Rotate (with modifiers key) to copy-rotate the geometry
Select all and intersect with selected
Cleanup! (remove interior faces, smooth/hide lines.