The Plagueworks Trash
To be fair, not all of this trash is specific to the Plagueworks, but it's still annoying. First up are the orbiting Val'kyr that fly around the central spire itself: these can be single pulled but you'll want two tanks for all the delicious add-spawning flavor, as they clone members of the raid who then run amok doing all sorts of bad things if they're not coralled. For instance, last night I was tanking one and one of the clones just ran up and stunned me into oblivion. It's a miracle I held aggro. I must just be that annoying, I guess.
After you get those two down, you'll head left off of the spire as you look at the map and head towards the two huge abominations guarding the path into the Plagueworks itself. If you don't want to have to tank a whole lot of adds at once, you'll pull those guys back a bit. Hilarity can ensure when, as an example, one of the abominations uses Scourge Hook on the tank, especially when it's the tank for the other abomination. Face them away from the raid, burn them down.
Then, of course, we have more trash. There's packs of geists but those are relatively simple for a warrior tank (grab em, spam every AoE ability you have, hit Shield Block once you're sure you have them, tab devastate a lot, wait for a warlock to go demon form and spam his AoE and die, laugh) and even less complicated for a DPS warrior (HIT HIT HIT UNTIL ALL IS DEAD HIT IT'S STILL MOVING HIT IT SOME MORE pant pant pant did we get any trash epics?) - there are also traps on the ground that summon more of these guys. Always be ready to either get aggro or to kill and kill until sticky fluids coat the tiles of the really rather wonderfully baroque floor. Seriously, the Plagueworks is lovely, in a 'place that contains horrible monstrosities around every corner' sort of way.
Once you get up the nice staircase, you'll want to wait to pull the Decaying Colossus first to get it out of the way. Well, who knows what you do. I prefer pulling him first. Tank him with your back against a wall so that the Massive Stomp won't push you back too far, or stand behind him and Charge/Intercept back when you get tossed. The really fancy trash in this wing are Rotface and Festergut's 'pets', each of which is basically Gluth. One of them, Precious, drops a green quality shirt. Stinky doesn't, which is probably for the best. Pull each of them out, tank swap once their Mortal Wound debuff stacks up (I'd suggest taunt trading at about five stacks) and be mindful of the Decimate, it's a good time to use a cooldown or trinket. Stinky has a raid wide AoE while Precious summons zombies (it's even more like Gluth) although she doesn't seem to eat them. We found it best to pull each dog down the stairs somewhat so as to not aggro the other and to have a ranged kite the zombies away from the group, but you can AoE tank them as well if your healers don't mind the increased damage you'll take.
That's pretty much it for the trash (there are Plague Scientists around but they're ridiculously easy to deal with) - just look out for the invisible traps and have a tank back near the door to catch the geists. From here, it's your pick of which hideously disgusting mutant undead you want to kill first. I'm gonna say Festergut because it's one of the best fights for a DPS warrior in the game.