I just installed a natural IMS 3 gal tank. I had a hard time finding a pic of the natural installed w/ the side covers installed too, so here it is.
I also marked mine as I filled it. I thought this might help those that don't want to mark their tanks. It might even give the folks w/ black/white/blue tanks a reference point for how much fuel they have left.
This was filled from empty using a rotopax 1 gal can in a (mostly) level garage.
1 gal line is pretty much even w/ the rear side cover bolts. 2 gal is even w/ the "WR-2" molded into the tank
2 gal is also pretty close to the line where the shroud wraps around the seat indent.
On the front, 2 gal is about 1/4 in from the angle change in the cover for the overflow tank. Unfortunately, I didn't find a good spot up front to see the 1 gal line. I'll have to look at that some more later on.
2 gal is also pretty much even w/ the top of the radiator cap.