I change coils every 4 or 5 tank fills and throw them in a zip lock bag. When I get 10 or 12 I put them in a glass of water with a denture tablet and let them soak for 8 hours, just enough water to cover them good. then take them out dry them off and let them set for a day and they are just like new again. I think the key is to not let them get too dirty/ burnt before cleaning them. But they seem to last forever before I have to rebuild them...
Wes