easy. shoot it in the belly, then when it's face is open, shoot it there, it'll push it back to the platform, and then once you are close enough, you'll get a prompt to push "Y" and notice the platform locks, shoot those, (2 of them) adn then into the emulsion it goes.
just watch out for the wretches that show up periodically, and watch out for the Corpser's attack (that's what it's called) that'll knock you back and injure you momentarily. also it'll attack with it's legs sometimes. i recommend using a shotgun as well.
and my gt=dkmarine but i rarely play gow anymore due to all the lil annoying whiny kids and all the glitchers/cheaters. takes the fun out of it and it gets old.