What is the best way to drain the gas tank on a 2003 Volkswagen Passat?

The Gas may indeed be getting to the engine but Gasoline loses it's volatility after sitting around for that much time. If the tank is near empty try filling it up with fresh gas, it will probably start. If the tank is full you may need to figure out a way to drain the old gas out and replace with some fresh gas. Let us know if that works.

Sounds like filler vent tube is plugged. Have a competent shop or dealer look at it, they'll either replace line or blow compressed air through it.

As a modern car it will run fine on any unleaded gas/petrol and the engine will self-adjust it's ignition timing to suit.

But some Passat variants can additionally take advantage of Super Unleaded, it's a total waste of money and offer no benefits at all for most models. As you haven't given further details of your exact Passat variant I cannot be any more specific, but the recommended grade is usually on a label inside the tank filler door.

This is your a sending unit in your gas tank.You will need to drive your car on ramps disconnect your battery.Now underneath the back rear of the car using the proper size socket your gas filler neck that goes to the gas tank pull it back.Now using a proper syphon er insert into tank with other end pump out fuel into a large gas can.Once you have syphoned out your gas it is time to loosen the gas tank straps.Have a hydraulic jack handy to support the gas tank as you lower it down.Now disconnect your gas lines and wire harness plug.You will need to remove the fuel pump sending unit retainer once removed you now have the sending unit in hand now reinstall your new or used unit and reinstall.Be sure to make sure all gas lines are connected and wires before you lower car of ramps.Return your fuel to your gas tank reconnect battery and now inspect for leaks and you should have a fuel gage now.

If there are no drain locks on the bottom of the radiator, remove lower radiator hose. To create a vacuum, remove radiator cap and upper radiator hose .

On the carter of a gear box are two plugs.For drain and another for oil level check.Bottom one is for drain.

There is a tank under the hood with a STEERING WHEEL icon on it. DON"T OVERFILL and use only PENTOSIN

make sure you do not have a bad cell in your battery also add some STP gas treatment to your tank to make sure you do not have a freeze gas line one of the injection could be plug so the STP gas treatment will help with that and the freeze line make sure you have over a half tank of gas in the car.

There is NO drain plug on the tank of that model.
John

there should be a pull cable located in the trunk on the side