I stabilize under vacuum. I use as much as my poor little vacuum pump will pull, right around 25 inches, perhaps a few more.
Honestly, I may as well not even have a vacuum gauge on the pot. Come to think of it, I may as well not have a pressure gauge on it either, since that is completely controlled by the regulator, but I am a curious person.
Actually, saying that I stabilize under vacuum oversimplifies it. I first pull a vacuum in an attempt to evacuate as much trapped air as possible. Then I put a pressure of about 60 pounds on it to try to force the goop into whatever I'm stabilizing.