It's like a very lenient kara throw input, if you have played a game that has those. The drill cancel essentially has three parts:
1. Jump, and hold down back. Quickly piano from K to P, making sure to hold down K while you are hitting P. (This cancels Faust's 2K drill move into Faultless defense, and causes him to float downward.)
2. Let go of down back and hit K again. This performs Faust's air K, which is what you want to hit the grounded opponent with. You want to hit this right after doing the above kara cancel, timed like a double tap.
3. Hit up to jump cancel the air K, then quickly hit down + K to perform the drill move.
Done correctly the air K will hit nice and low, and combo into the drill move. You can perform the kara cancel over and over in the air as long as you have tension, so you can practice by superjumping and repeatedly kara cancelling to float all the way down.
Drill cancel into far air HS is also fantastic if you have tension.