No need to use harsh chemicals at all. You can use a simple soap water solution in a spray bottle, spray it liberally on the window then scrape with a blade. Every tint shop I know of in Southern California does it this way and so do the techs over at Johnson Films and Sungard. As far as the rear window with the defroster line is concerned, here's a trick... Spray a LOT of the same soap solution onto the window (with the tint film still on it) then apply a sheet of cut Glad garbage bag to it, making sure the bag sticks completely. Then let the car sit in the afternoon sun for a few hours. You'll be able to peel the tint off relatively easily, but do take your time peeling it off. If there is some leftover adhesive, you can spray a liberal amount of Simple Green to it then scrub it out with fine steel wool. It won't mess up your defroster lines.