Left 4 Dead 2 Cheats

To get the achievement 'Tank Burger', you have to kill a tank using nothing but melee weapons. If you have The Passing DLC, then you should have the 'Mutations' game mode. There is one mutation type where you have nothing but chainsaws. All you have to do is get through the campaign until you get a tank. Once you do just run straight to him and maul him with the chainsaws until he falls to his death.