Yeah I just came back to post that I just completed the Man Vs Tank achievement, using a very similar method to what you said too.
Still, gonna go for "no friendly fire" now
Knocked that one off too
I only got vomitted on twice on top of that, I really think that that achievement and the no spec damage one will be pure luck. You seem to know an awful lot about these achievements, I'm guessing they're in the Pc version too?
Thanks man
EDIT: I managed to complete a campaign on it's hardest mode - and I didn't get the freakin achievement. Never mind, I will try again when I'm not too sleepy. I don't understand why it didn't unlock though, but still at least I know I can make it with 4 other players. These were randomers and it took about 1hr 20 to do the first campaign.
Playing it on Expert leads to a much more interesting game, these guys had gone through it before and I learned quite a lot in the time I spent playing with them. I found out things like:
Places where you can skip out on alerting the horde,
Which rooms are available to bottleneck zombies along the way (inc. the side rooms in the sewers, for example),
That pipe bombs are more a method of prevention than a reaction to being attack (I.E. If you're gonna cross large open spaces you can throw the bomb to lure the zombies away),
The favoured method of defeating a tank is to back-track through the level to an open area that you can do a loop in, so you can play ring-around-the-roses with it; like a horrofic benny hill scene (Like if one appears just before you enter the hospial you can drop in to the sewers using the side tunnels to keep distance from it)
Using Painpills much more efficiently (Stopping death rather than using it to stay alive after death),
How annoying it is when one char won't listen to anyone!
Just through playing No Mercy