Tank flying is very fun and also very easy.  It is much better to watch the movie instead of reading this, but I'll do both.

1. Go to Coagulation.
2. Get a tank.
3. Go up the side of the canyon walls (the one where the sniper spot is close to).
4. Now face down.
5. Go straight down and try to let the tank's nose hit the ground at a 90 degree angle.
6. Enjoy.

The tank goes spinning around like a top and bounces when it hits the walls and ground.

Click here for movie