Well, I plumbed the siphon bulb just below the fuel filter. With a whole lot of pumping the bulb, gas filled both tanks, but not to capacity.
There was still a lot of air in the lines.
Then it hit me!
The fuel lines to both tanks end with barbed fittings mounted near the top of both tanks. Fuel and air pushes thru the lines by squeezing the siphon bulb. When I release the bulb, the bulb sucks air back into the lines from the tanks.
I need to change the barb fittings to ones that will extend the auxiliary fuel lines to the bottom of the tanks, below fluid levels. That should allow me to easily fill both tanks, and maybe allow the front tank to siphon on demand.