Confident Boast: *****, the skulls of my slain pierce the heavens. I've whooped your ass in this thread. You've so far failed to come up with a shred of proof.
Condescension: Maybe you should go ask LeGenD for some tips. So far he's given me more pause than you have.
Nihilus was not taught how to drain from the Force. The KOTOR campaign guide points out that after he and other survivors were left on Malachor V, Nihilus (just 'the man' then) devoured the others to appease his hunger. Traya found him later.
Please post the exact quote because all other sources point to the sith assassins learning this from Revan, as well as Traya teaching them and Nihilus. The rest of the points still stand as far as Revan's underground tutelage.
First, it was I who allowed the alliance to know the location of the shield generatorwho brought that quote from the campaign guide to this message board's attention.
"An emptiness swept over the man's idle body and it soon began to "hunger" intensely. Without intent, he drained the life-force of another survivor. The act was an unpleasant experience for him, but for a brief moment the hunger ceased. The emptiness, however, came back more relentless and intense than before. He indulged in absorbing the energy of other survivors, but the more he fed, the shorter the hunger was appeased and the more relentless it became"
This is before the war's end with Malak's death. However, the implication is very strong that Traya helped him refine it.
I'm unsure of where Revan's been implied to know the technique, but I wouldn't really be surprised if he did. The Thought Bomb, after all, takes a lot of notes from Force Drain, and Bane uses the technique in Dynasty of Evil (he could, granted, has learned it from Nadd's holocron, Nadd being a confirmed user of the skill)
"It is a technique that is almost as old as the Sith themselves... it is a means of severing connections between life, the Force, and feeding upon the death it causes. It cannot be taught... it can only be gained through instinct, through experiencing its effects, first-hand."
―Kreia
I never said that you could not develop the ability, only that it cannot be gained through study.