try going in circles around the rooms in the lower lab but watch out for the teleporters that release zombies as well. the Pap stratagy is good if EVERYONE has a good gun and you have 4 players and the points to upgrade the guns now if 3 or less people try staying in the upper area and moving between the elevator to the lower one and vice versa ,this moves all current zombies to the lower and by doing this makes them come at you in single file and moving back to up makes zombies relocate again
thats a theory anyway i havent got any good match ups on five mainly little kids who steal kills and hog the box or i get LOBBY CLOSED