Start a new game in "Dead Air" under the Easy difficulty and select the finale. Once you have made it to the tanker, restock on ammo, grab a pipe bomb or Molotov cocktail, then answer the radio and start the gas pump. Once the pump is activated, run around to the right-hand side of the rescue plane and prepare to fight off the horde. A benefit of this position is that the horde cannot come at you from behind. When it is time for the Tank to appear, it will usually spawn on the far side of the plane. Run up to opposite side then run back and forth without coming around the plane to your side. Your AI teammates will not shoot the Tank when it is on the other side of the plane. By crouching you will be able to easily aim at the lower body from beneath the plane and take it down quickly.
The open area at the end of "Death Toll" is a good location to unlock this achievement. There is enough room here to fend off the horde yourself and deal with the tank.
