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I used generic blue washer fluid from a big box store (Home Depot?). Doesn't seem to have RainX or other similar additives. I have attached a picture of the actual gallon used. It was full when I started, so perhaps was able to add 1/3 of a gallon.
I was going to ask the same question about the Rain-X. Its possible that what you added reacted with what is in the tank and caused some gunk to build up on the sensor. I think the first thing I would to is just drain the tank completely, maybe flush it a couple of times with distilled water and refill (with non Rain-X). If you have the headlight washer system you can remove the drivers side front wheel and the wheel well liner. There is a quick disconnect on the line that goes from the tank up towards the front bumper for the headlight washers. Just pull that disconnect apart and lower the end of the tube below the level of the tank and most of the fluid will drain out.