There is a better way to get the swat tank. After you get it for the mission drive to the inport/export dock in SF. Now pick it up with the crane and lower it into the water. You will fail the mission because the game thinks the tank was destroyed. You can then take it out of the water and drive it to a garage. I used the hanger at the air strip and never had a problem.
I will wear the ass-less chaps, but it's going to cost you!