Vault 9000 - It has 9000 Atheists (all unarmed and 500 metres away from the tanks) and 100 angry Christians with tanks. (the tanks are impregnable, though the Atheists onluy figure that out if they get close enough)
Vault 9001 - There is one necrophobe, it is situated below vault 9000 and every person (all 9000 Atheists) that die in vault 9000 fall down into vault 9001. So, once vault 9000 is finished, vault 9001 will contain OVER 9000!!! (sorry I had to) occupants, only one of them alive.
Vault 10,000 - There are ten thousand people, all running one giant obstacle course of death. At the end of the obstacle course (for those who make it there alive) is an exit, but it needs a keycard. An announcement goes over the speaker saying that the keycard is back at the START of the obstacle course. They get the keycard, get back to the exit, use the keycard, and the door opens up ... to reveal the outside ... which just so happens to be on the other side of a lava pit with 10,000 narrow beams going across it (one for every possible survivor). Only one in five beams are stable, the rest snap when the survivor is half-way across.