Where is the rear window reservoir on a 1993 Plymouth Grand Voyager?

First check under the hood, there might be a separate reservoir for it right by the windshield washer reservoir. It might also be at the back, lift the tailgate and there might be a little cap with a windshield wiper logo. Or the rear window washer might work off the front windshield reservoir. If it's shared at the front, then you'll have to keep the windshield washer fluid above the middle line on the windshield washer reservoir tank at least. Open the rear hatch. On the driver's side, there'll be a filler cap which is used to fill the rear window washer reservoir.