You get an achievement for that!So, fastest way to down a tank?
I usually just punch it, while an engineer's level 3 turret does do some good damage. There was a situation where the tank got to the bomb site, and was unloading, before we just killed it.
Krit Heavy and Krit Demoknight are actually the two I've seen do the most damage. Have a Medic charging Kritz really fast and he can allow one class to easily do it all himself.