Please correct me if I'm wrong. I thought non-cal fuel tanks had only 1 nipple. It did not vent the tank. It was the drain line for anything that might get into the well surrounding the fuel cap.
That would be correct. The cap does the venting - it is only supposed to let air in so fuel can go to the carbs. Oneway diaphram construction. Under heat pressure, air does escape from the cap giving the bike the "singing" when she is parked. As far as I know, the drain line is the nipple slightly to the right side of center on the rear of the tank. You should be able to blow into it and feel air at the gas cap. The vent line I believe goes down the right side of the engine to exit at the swing arm (below by a few inches).
Follow this advice from T-Cro (if not all of it):
You need one line coming from the gas cap drain nipple on the back of the tank going down to the swing arm area.
Plug the remaining two nipples on the back of the fuel tank.