11g, 40s at level 70.

I soloed this as a level 70 affliction / demonology warlock without too many trouble. Here's a little guide:

Go to the back entrance of Dire Maul in Feralas. The location is shown on the map Burgermeal posted, and it's pretty hard to miss. Just look for a structure with the same design as Dire Maul and head through the tunnel. When you're there, either open the door with the Crescent Key or Life Tap / Hellfire and revive your spirit at the other side of the door.

When inside the instance, you'll see you skipped the entire elemental area of Dire Maul East and are at the demons you need straight away. Your Voidwalker is the one you'll love in here. First, you see two plants which aren't linked. Just pull them, drain tank a bit and they'll die without too many problems. Time for the real work now.

In the area you'll find a couple of patrols which you'll want to pull first. They're not much stronger than a regular level ~68 mob, so you'll hardly have trouble with them. If you've cleared some patrols, it's time for the packs. Stick your Voidwalker on one Satyr, banish the Betrayer and DoT + drain tank the other Satyr. When your mob is down, kill the mob the Voidwalker is tanking and then kill the Betrayer which should be unbanished by now.

This tactic will allow you to clear most of the area you need and should provide you with sufficient Satyr Bloods to complete the quest. Judging by the comments in this thread, many people seem to think there's also packs of four demons. This, however, is not the case. If you see a group of four demons, you'll see a normal group (of three demons) and a patrol. Just wait a second for the patrol to leave and do the normal routine. It might take a while for the patrol to leave, so don't bother trying four mobs at once (although it's probably possible), just head for another group or a patrol that isn't near a group.

The droprate wasn't that high for me, so I actually had to reset the instance once and kill one or two more packs. It took me around 1,5 hours to complete this quest.

Because I was in the demon area of DM East anyway, I figured it would be nice to try some bosses there, just for laughs. The first boss you'll encounter is Lethtendris who has an imp minion beside her. Just send your Voidwalker in, kill the imp (couple of DoT's and 1 or 2 shadow bolts should do) and then just Health Funnel your Voidwalker. If you have Siphon Life, keep it up to gain some extra health. I haven't tried drain tanking so I have no idea if that's actually possible, I just did it the safe way and do very slow DPS (the Siphon Life and sometimes a bit of wanding). You could also put an (amplified) Curse of Doom up, to speed things up a little without pulling aggro too soon of your Voidwalker. Once Lethtendris is dead, you can go downstairs and use exactly the same tactic on Hydrospawn. Both dropped a green for me, so I didn't actually profit from it, but it was quite fun, I guess...

Anyway, once you're done with this quest, and the Prison's Casing quest, head back to the questgiver in Blasted Land and do the final part.

Good luck!