I used to do this meditation for a long time and can confirm this method is definitely very effective.
I was "building" a while-gold ball of energy by vibrating a sun mantra or rune (usually Sowilo and Aum Surya) for 40 reps and then I was visualising the ball of energy entering my head and pushing all the dross downwards, so I was vizualizing the ball of energy being bigger in diameter than my body so it can engulf me completely.
Once the scanning was done I was visualising the pile of dross exiting my body through my toes and the ball of energy going in the earth through the floor. I was then saying the affirmation and vizualizing the pile of negative energy and curses flying away back to those who sent them. The meditation normally instructed to ask a Demon take the energy away though which is in fact the safer and more effective way of doing it.
However this meditation is very intensive in concentration and you must make sure you maintain constant focus on the ball of energy scanning your body (hence why it was taking me at the very least 20-25 minutes to do it). If your thoughts slip away and other thoughts start to intrude, always remember about the ball of energy and get back to it pushing the dross down.
This only gets easier if you have a good void meditation and vizualization routine done daily, because that is what directly trains the mind to focus on one action or one thought at once for a prolonged period of time, whereas the minds of most people are rather chaotic and all sort of thoughts fly in and out endlessly, whether willing or unwillingly.
You must feel, or "generate" the feeling of it going down your body and pushing the negative energy downwards and you can tell whether it has been effective or not if you get the feeling that all of the dross has left your body at the end. If you feel it hasn't, you can quickly visualize the rest of the dross left in your body in the same way, going down through your toes but using your will this time and not a second ball of energy. Push the dross itself down using your willpower.
Of course those with more developed phychic abilities can "see" the dross and at that stage cleaning is much more easier.
As a side note if you have a very effective AoP meditation and do it every morning before your day starts, you should have a smooth no fuss easy day.