tanks are fine for bp's. i just mention tubs cause sometimes people keep little hatchlings in these large tanks. you could just get a small tub set up for a couple months until they become large enough to live in a nice sized tank.

the problem i see with having a tank with a ball python in it is the fact that most of the time you will be looking at an empty tank. ball pythons spend 90% of the day in there hides and maybe come out alittle more at night. they are so shy if some one walks by they might get startled and whoop! back in the hide they go. I had my ball in a tank for months. but with humidity and temp problems, and the fact that everyone that look in to the tank always had to ask "what's in here?".