Yeah, you're right. I don't know anything about physics.

The muffler pressure will make the fuel flow from the rear tank to the front tank (unless it is some extreme distance and the hydrostatic head of the column of fuel in the line is too great for the muffler pressure to overcome). The front tank is never depleted of fuel, and it never has to "suck" fuel from the rear tank. It is fed fuel from the rear tank.

A good example where you can actually watch this happen is a heli running a header tank. Some helis have the main fuel tank quite a bit below the optimum elevation for the engine to maintain a consistant neddle throughout the tank. They run small headers close to the engine and at a level that allow a consistant needle. This set-up draws fuel "uphill" for extended periods and the mixture does not change until the header tank gets close to empty.

I've run this system on both helis and planes, and it works just dandy.

But then I don't know anything about physics..maybe that is why it works for me, I am just too stupid to know any better.