What I did was mixed up a solution of bleach (the dilution on the side of the bucket) and put the fake coral in it for a while (say 15 mins) and then scrubbed it. That was white coral. I then rinsed it very well, extremely well. I then let it dry, then rinsed very well again and let it dry. I then pu it in the tank.
Maybe a bit paranoid but didn't want any bleach in the water. I would not suggest this method for coral that is not white cause it may take out the colour.
Good luck man.