For fuel to enter the tank, air has to release. There is a vent for this purpose. I believe on the 99 A6 is runs along the side of the filler tube up to where you fill the tank. Air comes out of it while the tank fills. If the vent is damaged or plugged, it will not allow fuel to enter the tank unless you put it in slowly allowing the air to escape through the filler tube. Check the vent to for damage.
I just found a picture of the tank set up. It has a total of 3 vents. Two go to the EVAP system and the other is on the side of the tank. Audi doen't allow me to copy and paste the picture for you so I'll try to describe it. If you are facing the filler tube, the vent in question will come off the top of the tank on the left side of the filler tube. It should run to the filler as discribed. Check to make sure it isn't plugged or damaged.
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Monday, January 17th, 2011 AT 5:10 AM