I just cleaned all of my old coils... so far have only vaped on one of them and it's giving great results... I just soaked them in hot tap water for about 2 hours with just a couple of drops of dawn... just make sure you rinse the hell out of them after the soaking to get all of the soap out of them. Then let them dry for quite awhile before putting them back into service...
I've got the temperature controlled istick 40w so I just turned the temperature down to 350 so I wouldn't burn the cotton and pulsed it for a bit to get all of the water out...
I've also heard of people using Everclear or Vodka to soak them and the tank parts in for cleaning... Don't use rubbing alcohol...