Originally Posted by Mat_te_chu
As far as I can tell it switches, because while the tank sticker said 60 gallons fuel capacity, I could only go through 15 gal of gas before my fuel gauge read empty.
Now we're getting somewhere. Very few school buses have two fuel tanks (not to say yours doesn't, but it would be a rarity). In most big trucks these days, there is no switch. The system is designed to simply draw from both tanks at the same time, and the tanks will equalize themselves without any action on your part (many older systems had a cross-over line for this purpose, and even on today's newest vehicles the pick-up tubes serve the same purpose).
Now if you're using 15 gallons before getting an empty reading, I would check the tank to verify it is actually indeed empty. You may be getting a bad reading from a faulty sending unit.
Have you looked and verified the bus actually has 2 fuel tanks, and more to the point, there is actually a select switch? (I would not necessarily expect to find one)