There's really no reliable way to incapacitate any vampire that's higher than generation 5, in my experience. You may be able to /kill/ them in certain situations, mostly with explosives, but their pain resistance is so absurdly high that they won't go down until they're dead, making diablerie essentially impossible.

As for digging, that's an automatic behavior that vampires do when they've been in sunlight long enough to start panicking, or can't path back to a shaded area. There's no way to perform it manually, as far as I know. The closest you might be able to do is put down some sort of coffin and have them enter a torpor state, which is essentially the same thing with a different container.

Psychic shock Lance maybe? Incapacitated it and suck it dry?

step 1. Psychic Shock Lance

step 2. Anesthesia

step 3. Diablerie