This is the daily quest that becomes available after completing Basic Chemistry. It's basically a repeat of that quest - kill a Pustulent Horror, have everyone in your group loot the spine and use it to convert it to a Pustulent Spinal Fluid.
Head inside Mord'rethar, find a cauldron and use the fluid on it. Once the fluid is used on a cauldron, waves of mobs will spawn and attack until the cauldron is neutralized. Spawned mobs will randomly be one of the following:
- 8 x Living Plague (12K HP each)
- 2 x Rampaging Ghoul (25K HP each)
- 1 x Plague Drenched Ghoul (65K Health)
- 4 x Living Plague and 1 x Rampaging Ghoul
As stated above, using the fluid is channeled and any hits from mobs will break the channel and start the cooldown for that player, so ideally you'll want 3 people - one to tank the spawns, and two others to alternate using the fluid on the cauldrons. It can be done with 2 if you can burn through (or taunt) the mobs fast enough - but leaves little room for error.
Sometimes the cauldrons bug out and become unusable until a server restart or maintenance, so if one isn't working try the other two.
Finally, the Living Plagues drop loot - coins, cloth, potions, food & drink, vendor trash and the occasional green item, so don't forget to loot them!