I'm a little late with my two cents but I thought I had this problem with my car when I first got it. So I ordered a new washer tank and went about installing said tank. It lives in the fender well behind your right front tire. The wheel well liner has to come out, I removed the right front wheel for more room. What I found is that there is a separate fill tube (what you see in the engine bay) that plugs into the actual reservoir. When you add enough fluid to reach that junction, excess fluid runs out at that joint as it is not sealed. My reservoir was fine, I just needed to learn not to try to fill all the way to the top of the fill tube.