How do you refill 2002 VW Passat wagon rear washer fluid tank?

There is no separate reservoir for the rear fluid on an 02 Passat Wagon. There are a couple reasons why your washer might not be working: 1. a hose came disconnected (very common). Open the rear hatch and remove the side panel cover on the drivers side. This access panel is marked with a red triangle. Reach up into the compartment and you will find a small hose. This hose delivers the fluid from the front reservoir to the rear washer. An elbow in the hose regularly comes disconnected, or breaks. If this has happened, you will probably see and/or smell washer fluid in this compartment. Re-connect the hose and this should fix your problem, at least for a while. 2. your nozzle is clogged. The nozzle is located at the base of the rear wiper. There is a plastic cover that can be pivoted out of the way to access the nozzle. Pivot this cover towards the wiper blade. The nozzle will pull straight out using your fingers, or (carefully) with pliers. Clean the nozzle by blowing compressed air in the normal direction of flow, or by using a fine wire to push out any contaminants. I'm not sure but there might be a small check valve (one-way valve) that might make it feel like it's clogged. Don't be too aggressive in cleaning, just try to remove any crud in the tube end of the nozzle, reinstall, and try it out.