This only works when you play online. Play vs mode and play at the drains.

As the survivors open the safe room door a tank should come. The person who is the tank just stand there and lose control of it.

Keep doing so until the tank is controlled by the AI. The survivors stay in the safe room and wait for the tank to come.

When the tank comes kill it. Because the tank is in the safe room another tank will spawn outside the safe room.

The tanks will keep on spawning until you die.