Hands down the easiest way is:
- Dead Air (Finale Only to get you full health/ammo)
- Solo (maybe 2 player co-op)
- Play as Zoey if you are solo, as normally she whores out the sniper.
- Have mad skillz (you don't really need them, only quite a bit of luck.
Then basically follow this video. It should take 5 tries maximum.
Just make sure you clear out the area of zombies, and hopefully a pipebomb spawns to help out for the final run.
This doesn't require any glitches, just stay back and use your shotgun and pistols, rush ahead to lure the tank and strafe it/force it to throw the slab of concrete against a pillar.
Good luck, if you get it then you will the satisfying sound and it will pop up just before the credits.