Originally Posted by Some Dude on a Ski
when on the water, the Aux tank drains 1st, leaving the main tank reading full until the aux tank is empty and venting air into the main tank instead of just replacing gas. this eliminates the need to open the fuel cap while on the water and holding a 5 gallon jug precariously over the front of the ski in chop. this method also removes the need for electric fuel pump transfer, or hand pump....as you use it from the main, it just refills from the aux.
I will also follow this thread with great interest.
On my dory, I have a fuel filter w/ two inputs and dual ballcock valves. I monitor and manually switch between the two tanks. The simplicity of this dual tank design is ingenious, having no moving parts. The only precaution is the main tank must remain tightly sealed for the system to function correctly. To remove the AUX, just swap the position of one vent hose and quick-disconnect the aux fuel line.