I can't tell you the exact location, but it shouldn't be too hard to figure out. First, does your boat have that option? Next, where is the actual tank? Fills are usually pretty close to the tank. Find the tank, follow the hoses. Look for a possible access plate as the tank could be below a screwed down panel. If you still can't figure it out on your own, information like this is typically in an owner's manual. If you don't have it, download it from GW's site. It's gotta be 22' one way or the other!