I have found the best way to complete these fifty waves of horde, with one or two people. Go to the large building in the centre of the map that has the Grinder ontop of it, jump behind the bar where the boltok/gorgon pistol is and you should have two metal frame kind of things that have what looks like a washing machine/dish washer in them. Go to the back of this and set up two shields blocking yourself in. I found it works best with two people. You are near enough untouchable from anything here (maulers, bloodmounts ect.) Don't sit right at the back as a boomshot may get you, use the shields for cover to stop any ememies knocking them down. The only possible flaw is kantus throwing inks, make these your first priority to kill and you should be fine. For even more security get two more shields and block off the two openings to the bar at each side. Enjoy.