It's exactly this problem that I have created an account with this website!!
My driveway slopes too and had the rear of the car pointing down it and had the left it there for a few days after working on the interior. Went to start it to go to V and petrol went everywhere. Quickly turned ignition off and pushed car back into driveway. Drove it again a few days later and,...nothing.
Drove it again and then the leak was only slight,not the zoom juice flash flood as before.
Unfortunately no mobile vw specialist in my area and car due for MOT,have to drive it to garage,no choice (will get the old man to follow me on motorbike armed with fire extinguisher!)
Thanks for your help buttles!