In the level 80 only zone of Orr, there are Veteran Risen Giants which spawn around 4-6 risen grubs every couple of seconds. You can use ranged weapons to have the giant enter combat, kite it as it moves slowly, and kill the grubs that the giant summons which drop venom sacs and other loot such as blues and greens. Just make sure you don't let the giant get into melee range, and it tends to stand still when it throws up locus at you. I've only farmed on the giant west of the skill point in Craven Blight, and it is NOT an event giant. It's a very fast farm rate and the giant respawns every 2 minutes or so if you accidentally kill it. These grubs are fast spawning and take around 4-5 players to aoe down efficiently. The area that I named was fairly safe as most of the mobs were spread apart. Best done with a group and MF!
Summary: Kite veteran risen giant --> kill and loot spawned grubs --> rinse and repeat --> ??? --> profit
Sorry if this was in elite... I can't see elite :/
Location:
EDIT: After running in circles around it as with signet of malice + shortbow + bladestorm, thieves could actually farm this pretty decently as long as you don't get poisoned. The giant literally just sat in the middle yelling at me and the grubs missed their attacks 60% of the time.
EDIT 2: With 40% MF, 1 giant lasted around 20 minutes (some players randomly came and helped) and I got 1 rare, 4 greens, 3 blues, 2 400crafting sac, 18 325 crafting sacs, decent amount of salvageable whites and a lot of porous bones greys.Very good for farming sacs!
EDIT 3: The one that I posted in the map is the best to farm as it has more hp compared to the other (non-event) veteran risen giants, so it lasts longer.
EDIT 4: If the grubs stop dropping stuff after a few waves and you've been there for more than 20 minutes, anti-farming might of kicked in, so you gotta go do stuff elsewhere before loot drop normalizes again.