Fighting the tank is a huge event in Left 4 Dead, and there are several schools of thought on how it should “best” be done. On difficulty levels used by reasonable people, the team can just focus fire on the thing to bring it down. On expert level, a single hit will incapacitate a player, and afterward the tank can easily finish off the helpless player in a couple of hits. This means that fighting a tank is pretty binary. You either escape unharmed, or it ends your life. Oh yeah: He can rip up huge chunks of ground and heave them at you, and these masonry missiles have an annoying habit of reaching slightly around corners and striking you through non-static scenery. (To put it another way: Homing rocks that pass through cars.)
The common approach to kill this musclebound cheater is to set his ass on fire. It puts him on a timer that will kill him in under a minute, no matter what. (Even if he ends up in water and the fire goes out.) On the other hand, he runs faster than the players when he’s burning. Lighting him up increases the chance that someone will die, but decreases the chance that he’ll end up killing everyone. It’s an interesting tradeoff.
You can do well by making lots of vertical changes; the tank is slower at hopping up and down than players. You can do even better by sacrificing one of your teammates in order to secure your escape.
Shamus Young is a programmer and writer by trade, videogame nitpicker by inclination. If you have the patience for more of his ramblings, they can be found at ShamusYoung.com.