You need the speed of Unholy presence and the Glyph of Disease, which refreshes your diseases on the main target. Here’s the rotation, which is simple as can be:

The setup (Pt 1):
IT>PS>Pest>HS>BB

(Pt2)
You either auto attack ONLY or toss in a couple of DC’s before resuming with the real meat of the rotation here:

(Pt3, use when runes reset)
HS>Pest(resets disease timers)>HS>BB

Repeat parts 2 and 3 over and over until mobs are dead.

As a 73 I intentionally rounded up 4 74’s and was getting beaten on while rounding them up. I was at half health when I fired off the first hit, the IT in part 1. By the end of the fight, all four 74’s were dead at my feet and all those HS’s had slowly worked me up to 80% health.

And that’s the whole key, MOST mobs you will take on, even 2 or 3 at once, can’t damage you as fast as all those repeated HS’s are healing you. It works because you no longer have to take time to set the diseases over and over since you have the glyph of disease!

Well, that, plus the fact that Unholy Presence allows you to attack like a rabid machine gun!