Hi can you tell me where to find the rear windshield washer container to fill on a 99 gmc jimmy

I had the same problem. Under the hood right, side front: The motor for the back windshield wiper fluid is above the motor for the front windshield wiper in the same tub .Possible reasons why back washer doesn't work--either the motor is bad and needs replaced or the fluid level in the tub has dropped below half. When that happens the back motor won't run the rear washer.

I'm pretty sure it's the same as the front washer, You can check by see ing if there are two pumps in the front washer resevoir, if not there is a possiblity that there is a bottle in the back, servicable by opening the rear door and looking at the walls behind the tires. I hope this helps