Fuel tank is plumbed in. The plumbing is as follows.
A vent/return line was added using a blind bulkhead fitting on the right hand aft corner of the tank. This line connects near the top of the aux tank.
The fill/drain line is connected to the bottom of the aux tank. From there it runs to the aft end of the main tank where it connects to the pump and valve. The connection to the main tank is made on the main fuel return line after the fuel cooler coils and thermostat.