I think he was asking about my XT tanks, which are the older kick start US models. They have 2.7 gal capacity approx. with .5gal reserve. If he is in the US I think the E models have a 3.7gal tank +.5-.75 reserve.
I don't wait till I run out going down the road and try to get the switch turned to reserve before have to stop in traffic. I usually just fill up after 80-90 miles , there is no good reason to just run the tank empty unless your on a trip and simply can't fill any earlier, or want to run all the fuel out to clean the inside or change petcock ect....