Quattro fuel system

http://forums.tdiclub.com/showpost.php?p=4707185&postcount=31 got me thinking about my 99 A6.
Before I rolled it in the garage the last time, I parked my truck next to it, stuck a hose on the fuel line in the engine bay and hot wired the girl pump to run, intending to empty the tank.
After reading this thread, I stuck the supply and return hoses together and ran the pump. It gurgled and belched for a bit, then found more fuel. I'm not even sure how mm ugh gasoline is still in it.
I had intentions of doing the H pipe thing. I measured the back pressure from the venturi pump at 21 psi.
How does a factory diesel manage this issue?
Does one of those vapor lines dump back to the tank so that I can use it for a non back pressure return?

bump..

I'm not sure how the factory diesels handle it, never seen one of those tanks.

The vapor line could be a good easy way to return the fuel, but you'd have to check and see if they have any valves/restrictions. You'd still need something pumping fuel to the venturi pump, or else you'll run out of fuel with a good bit still left in the tank. Fuel on the drivers side of the driveshaft will be unusable.

My method of using a second pump is a bit clumsy, but it works well and was free since I already had an extra pump. You could potentially use a returnless regulator at the tank, T the pump output, fuel return to the venturi, and input to the regulator together, then use the output of the regulator to feed the engine if it's low enough. If you can't find one with a low enough output, the output of the returnless regulator would need to feed another regulator that gives the correct pressure. That's the best way I can think of at the moment to accomplish it with one pump.