The only thing I have found to successfully remove Rain-X is Permatex GS8 Auto Glass Stripper. I ordered mine from ACE Hardware online and picked it up in-store. 1 or 2 applications of this stuff did a good job removing Rain-X, while also cleaning the windshield of any dirt, debris, etc. Previous to the GS8, I also tried (unsuccessfully) Dawn dish soap, isopropyl alcohol, and a dish sponge with Comet. Some of these helped a tiny bit, but only minimally. Do a google search for the GS8 stuff. IIRC it was less than $10, and does a great job cleaning glass, including the removal of Rain-X. Maybe try clay-barring your windshield? I know Rain-X bonds to glass, so maybe the friction of the clay bar would aid in the removal, but this is only speculation. Can't hurt to try if you have a clay bar lying around.