If you painted the tank when there was high humidity, the tank could have "blushed". As the solvent is evaporating from the freshly applied paint, the surface of the paint becomes cooler than the air temp. When this happens in high humidity - the cool surface of the paint can cause the humid air to condense water onto the surface, and this can result in the paint getting a hazy surface instead of a gloss.
If the finish is smooth (no runs and very little orange peel) - then sanding is not necessary. Buffing is done with a polisher, and most polishing of the 2K paints is done with a foam pad (enamels and lacquers normally used a wool pad). You start with a a buffing compound and a stiff foam pad, then use a polishing compound on a gentle pad to remove the swirl marks.
I recently bought the Harbor Freight buffer and I was surprised how well it works.....I gave my 30 year old 1 speed buffer away after using this Harbor Freight buffer.
http://www.harborfreight.com/7-inch-electronic-polisher-66615.html#reviewsThe large 7" pads are great for cars - but for motorcycle work I bought some 4" pads as they give better control. You won't keep the compound from flying around, so it is best to throw towels or blankets over anything you don't want to throw some compound on.
This is where I get my pads....I buy the compound at the local auto paint store.
http://www.autogeek.net/I would suggest you find a paint or detail shop and ask them what they would charge to buff it......that will save you from buying $ 100 worth of supplies to do one tank.
Or....I can bring my stuff to one of the Dragon Runs (or if you come up to KY in August), and we can buff the darn thing!