K so, I was fooling around on my rogue quite a long time ago. Since the patch this has gotten way harder to get to the third barrel but I JUST did it so it is possible, though extremely hard. I also did this on my priest so I could mind control people but then realized I only get up to 30 mind control..
Jump straight forward from here.
Try to get onto the barrel, may take a few tries, took me a ton of tries.
Jump to the next barrel, I didn't have a problem with this part.
You have to try to get stuck half way up the pipe, then jump again. The jumping method I use is hitting space and forward at the same time. Not sure if this is a common way, just the way I do it.
Now that we are here, there is a very easy jump to the next barrel.
There you have it, I haven't tried killing alliance from here due to the fact no one goes under it, and I'm too low of a level on my priest (31) so maybe you'll have better luck. I'm well aware this is my first contribution, but I didn't see it anywhere on the forum, so here it is.