All you need is a molotov and a machine gun/sniper rifle.

When the tank comes throw the molotov at the tank and run away, stay as far away as you can to prevent the tank throwing concrete at you.

You can then begin to shoot from range which is why you don't take a shotgun because you simply will not cause enough damage. The tank should be at a minimum of 3/4 health so it is simple to finish him off if the molotov doesn't kill him completely.

Tip - for an added boost when running away take an adrenaline shot.

Warning - if attempting this on single player, computer controlled bots will run towards the tank and begin shooting, leave them to it and escape yourself.