If you mount a fatbob tank on a Sporty there is one thing you need to do that they don't tell you about. I re-wired the bike so it used a stock Softail ignition switch up on the tank. The Fatbob tank kit (from V-Twin products) gives you a Softail dash and ignition switch but it's only supposed to be for looks.
I decided to get rid of the wiring in the headlight and actually use the tank mounted ignition switch. The problem I ran into after the bike was all together and painted was that water stayed in the top of the tank indentation where the ignition switch sits. It's like a mini fishbowl up there.
I took the tank off and had a radiator shop weld in a small piece of 1/2" round stock that I cut to use as a drain tube. It only has to be about 2 inches long. It goes from the back of the dash cutout on top of the tank to the bottom of the tank where the backbone runs up the tank. Now the rainwater will drain out. I don't have a picture because the tank is out getting re-painted, I didn't use "gas-saver" inserts around the filler openings and the paint started to bubble up