Scout Knowles at the Ember Spear Tower has recommended that you use the Ever-burning Torches to destroy the four Plague Tanks surrounding Halgrind.
1x Southwest Plague Tank Destroyed
1x Northwest Plague Tank Destroyed
1x Northeast Plague Tank Destroyed
1x Southeast Plague Tank Destroyed
The Forsaken are up to no good and from what I can tell, those plague tanks of sludge are a big part of it.
If I may suggest, $g sir : ma'am;, we should probably destroy them before they can get any more use out of the things. I took the liberty of preparing a bundle of torches from the Ember Clutch. These things have been burning for days!
Here, I'm sure you can put them to better use than I in destroying those tanks.