Agree on using Anzu's with either WUE or heirloom. If you use WUE and eat the first thrust and Guard after, be sure you're topped off first. That's easy if you're standing still. You can reliably top yourself off with EH and orbs (and Guard if you've screwed up or had terrible RNG with EB stacks or failed dodges). But if you're two-tanking and running around for Doomlords and you're also expected to soak a lot of Wrath stacks, then it's tougher. The second Doomlord, I think, is too close to the transition for me to use DM or ZM and have it back up for Wrath (I soak the first few dozen stacks from 4 dps). That leaves one Guard for the second Doomlord's debuff and only one for the next combo. Doable, but very little margin for error or bad RNG. For extra safety, you can just run the heirloom trink, and the extra shield fills the gap. So I run Anzu's with either WUE for extra challenge and fun or heirloom for extra safety.
All this said, you've killed Manno and I still haven't. So who am I to give you advice. Though in my defense our issue is not tanking. First it was failing to settle on a strat for something like 100 or 130 pulls. Now it's healers and DPS failing mechanics and DPS under-performing. Oh and also: not trying. We farm half the time, as if a tiny ilvl increase is going to make any difference, and now we wipe insane amounts on farm bosses because as people get frustrated and drop out and the raid group turns over we have new people who haven't killed the farm bosses before. Last week we spent almost an entire night wiping on Xhul, which we killed 2-3 months ago. Then virtually no one got good gear anyway. All this stuff increases frustration and makes more people quit. Rinse, repeat. A couple of weeks ago I would have said we're ready to kill Manny any night. Now I'm growing concerned we'll never kill another boss and I too should have bailed a while back.