Audi's especially the newer one's are a common site in the fuel draining industry.

And since Audi has become trendy and started doing some very sleek car's, the job has become a little more sophisticated than it used to be.

New Audi's especially the "Q's" require specialist knowledge to drain completely, reason being is the tanks  have 2 cells and balancing pumps inbetween, sucking out of the filler neck will not empty 1 of these tanks, and the brains of the car need to be bypassed to over-ride the balancing pumps to get out every last drop

This is a Q7 fuel tank

When you compare it to an Audi tank from the 80's (below) you can see how far more sophisticated they have become.
A nice simple tank that can be emptied by suction alone