Tanks have a couple of moves that you need to avoid. Its the other zombies around you that's going to be a problem.
To go with the crowd on this, a molotov is necessary but it won't cause a large amount of damage, it'll zap small bits of health over time little by little. On Normal a tank can survive at least one Molotov. If you have a shotgun you're going to have to be slightly closer to get the full effect of damage. You'll be able to give it more damage, but you'll also be within range of the Tank itself. If you don't have a shot gun then distance is your friend. You'll still have the damage deterioration of being far away but you'll also be safer.
The tank has three attacks that you'll have to avoid or deal with most often. He'll swipe at you. Often times this means he'll close the distance between you and him. He'll swipe at you as he's mid run to you. Its hard to time but you can almost bate him into attacking you. I'll say that its kind of dumb to try this without a shot gun (tactical is one of my faves for this) because he'll likely hit you and then get another hit on you after that.
The second attack is his distance attack where he tosses a rock at you. This is easier to avoid, but if you get hit he'll be able to close distance and hit you.
If a survivor is downed, the Tank will essentially pummel the survivor until their death. This is a good chance for teammates to kill the tank, but on a difficulty more than normal I'd say that the survivor is probably going to die.
Keep your distance and use the terrain to your advantage, but there's still times when a Tank shows up and destroys my team and I and we've been fighting the Tanks since the very beginning.
