Engine Plumbing in Gambit
 

I'm trying to model an intake plenum and runners for a 4 cylinder engine. I've been able to model T-junctions by joining two perpendicular cylinders, but I cannot model Y-junctions successfully. The Y-junctions are supposed to look like 2-to-1 collectors. I have tried joining two converging frustums to a cylinder, but this hasn't worked.

Also, I able to sweep a circle along a curve to create bent tubing. However, I want to create bent tubing with a decreasing cross sectional area. It won't let me revolve a curve around another curve. Is this possible with Gambit?