The in-tank screen is in the bottom of the fuel tank. The fuel feed line is threaded into the screen and can be located by following the fuel line that is located just above the diff (under the car). Drive the car as far as you can without running it empty and then pull the rubber lines from the hard lines (return and feed) on the chassis to drain the rest. It is a mess, but a 5 gallon bucket catches most of it. Fuel will drain onto the diff and then go everywhere if you're not careful! A 19mm fitting screws in to the screen and I found that when I began to loosen the 19mm fuel line fitting, the whole screen came out with it, which works out great! I just cleaned mine with carb cleaner and a toothbrush and it was good to go. I also used my finger to clean out slime that was gathered around the screen opening. Here is a pic of the screen to give you an idea of what to expect.

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1995 E300D - 193K and $28K in maintenance!
1964 220Sb - 318K, second owner
1997 Passat TDI - 190K and 47mpg