The outlet on the lower passenger side is actually the exit for a tube that
originates in the center of the fuel tank.  That low round spot in the center
of the tank sits a fine mesh screen that blocks trash from getting into the
fuel line going to the pump. The return line also has a fine mesh screen to
prevent any trash from getting out the return line.

Tilting the tank only keeps more fuel in the tank because it cannot flow out
the tube inlet that is above the fuel level.  To drain it without taking it
off, the best way to get it all out, keep it level.

So, Steve if you tilted the van, you still have water in the tank...that
could explain why the extra fuel pressure made it run better.

Robert