On the outside, Sprayway Glass Cleaner that can be bought at Costco. It works well, and typically doesn't leave any streaks. On the inside with tint, I use water and wipe it with a paper towel. It's typically recommended to use water or water with mild soap for tinted windows; at least most tint shops recommend so. As for privacy glass, I don't know if cleaners will harm them, but to be on the safe side, I'd use water. The inside of the windows typically don't get dirty enough to need to use anything stronger.