Here's what I did
Did this on a boat with a small main tank. Used quick disconnects and made sure to get enough fuel line to go from the aux tank to the engine quick disconnect. Aux Fuel line had a bulb in it. I just added the disconnects in line and clamped with SS clamps. Made sure the disconnects were at the transom area. When I ran out of gas in the main tank, just disconnected the main line, connected the aux tank line and pumped it's bulb. Took a matter on just minutes. No problem with leaks.
Disconnects run about $5 each. Used a small 6 gallon plastic tank.
Hope this helps.