For goodness sake, don't use isopropyl alcohol to clean your attys or cartomizers. For one thing, contrary to what I've read here and based on my limited experience, you never completely get the isopropyl taste out of the atty. Secondly, if you accidentally vape any remaining iso alcohol, your body will regret it.
Boiling is only good if you don't overdo it. Five or six minutes is fine, longer is not. I don't know if there's glue in there that melts or what, but bad things can happen. I had the coil/wick of three cartomizers sort of unwind themselves after boiling too long.
Here's what I do:
* Changing flavors: Drip some pure PG into the atty and burn it off. It's okay to vape it (unless you're allergic to PG). When the old flavor is gone, you're ready to try the next flavor.
* Rinse your atty in lots of hot water tap water) and gently blow dry using your lips/breath on the threaded side, blowing out the atty **gently**. Then, place the atty in grain alcohol. Here in Minnesota, the closest thing I can find to PGA is a 151 proof/75.5% Everclear brand alcohol. It seems to work fine. After a long soak (depending upon how dirty they are), I let them gently air dry overnight. Works great.
I am suspicious of cleaning with vinegar, lemon juice, isopropyl alcohol and/or mouthwash, because I don't think you ever get the flavor out of the atty. PGA evaporates completely, it doesn't hurt to vape a bit of it, it doesnt affect flavors you drip after cleaning with it, and it's cheap enough to use at least once a week to keep your attys in top shape.
I resurrected the Immortal, a 510 atty that I thought I had killed with J.C. juice, followed by some really strong flavors including my now-patented, horrible mix of menthol/regular/blueberry waffle. No, I didn't mix the juice together deliberately; I was just dripping, grabbed the wrong bottle and pow! Nastiness Forever. The atty was also dead b/c of the connector having worked its way up inside the atty housing.
Loxsmythe instructed me on how to fix that, but the larger problem was that the dang thing was gummed up with heavy, nasty juice and strong flavors. Grain alcohol saved the day!