OK, thanks guys. I had to sketch the UAT out on paper to better understand it. It appears that both the tank and fill line fittings are at the top of the container, and above the fuel level inside. Whereby the line feeding the pump comes from the filter element and remains submerged. So if I continue to crank the tank completely dry, and suck air, the membrane in the UAT should remain submerged, since the suck line fitting is at the top, and above the fuel level in the UAT. It will be sucking air from the tank, and not the UAT. Using the fill line to suck fuel from the tank, makes it seem impossable to ever empty the UAT. I think this is what George is saying, but saying better.

Thanks for helping out this newbie.