I have a wagon which has had this problem before. Even with the resivoir filled, nothing gets to the back window, even when I hear the motor running. I remember having this happen before and all my mechanic did was plug a hose back in. I checked the hose behind the right hatch hinge and under the rear tweeter and it seems to be plugged in correctly. I vaugley remmeber him talking about the hose being disconnected under the car, where would this hose be, and where does it go through the car.
Thanks