I've tested the practical limits of the fuel tank capacity before, did it in an area with plenty of fuel stations so I didn't have to walk far when I ran dry. The total fuel tank capacity is 4.8 gallons, though in practical application, once you've burned 4.6 gallons, the remaining fuel rests in the bottom cavities of the tank away from the petcock. So, I'd say 4.5 gallons is a safe number to run calculations off of. Remember, that number is including reserve. Without turning the petcock to reserve, you're looking at about 3.6 gallons. This is all with the bike on the side stand, filling up until the fuel is part way up the bottom of the filler neck. That is, when the top level of the fuel reaches the bottom edge of the filler neck, keep going another quarter inch or so. The goal here is that when the bike is upright, there will be just a tiny bit of an air gap between the fuel level and the bottom of the filler neck. The gravity feed system on these bikes don't need much air space for the vents to breath correctly.
On to your initial question, is 220 miles pushing it? Generally speaking, yes. Commuting around produces, at least for me, an average of 45-48mpg, which includes a health does of all types of riding. At worst, I'll run dry just after 200 miles. At best, I'll be sucking air right at 220.
For trips with mostly freeway riding at moderate speeds, say 70-75, I typically return 50+ mpg. That would get you past the 220 mark, though not comfortably.
If you're taking back roads and keeping a spirited pace but not totally romping on it, upper 40's is what you can expect, which would get you a little too close for comfort to 220.
For maximum fuel economy, riding at a consistent 55-60mph can net upwards of 60mpg. That would get you well past 220, 250 even. Best I've ever managed was 63mpg. Fuel economy like that would allow you to cover damn near 300 miles on one tank.
Lastly, if you're in a pinch and you've run out on reserve and the next station is only a mile or two away, there's one last trick up the sleeve. A small amount of fuel will get stuck in the lower right side of the tank. If you lean the bike way over to the left, that will allow most of that fuel to slosh over to the left side where the petcock is. This will allow you an extra mile or two, 3 if you've got a tailwind.