All you really need to do is get a big enough horde of infantry and let those assault the tanks from cover, just hide some melta bombs and power fists in between and you should have them immobilized and destroyed in no time at all.
If I were to tackle it as a Guard player I'd stock up on what Van Evok said, maybe paired with another command squad for "Bring It Down!" and enough Vendettas to help immobilize those beasts before the veterans move in for the kill.