I noke Johnson's Creek "Tennessee Cured" - a PG based, semi-sweet liquid. To this I add some extra PG 48mg unflavored for throat-hit and a dab of veggie glycerin for vapor. My coils get pretty gunked up. I can get a "fair" clean by soaking in isopropyl for a few days, scraping lightly with a very thin implement like a guitar string, followed by a burn that starts with peroxide squirted in with a syringe and once burned off becomes a "dry burn". After all that, I swirl them around in super-hot water from the automatic coffee machine at work. The alcohol always ends up brown from the juice and I always see lots of little black specks of carmellized juice in the water.
I investigated further with these atties: I dry burned them and verified with a microscope that the Crest had indeed clung to the coils. Hard to miss the light blue crystallized junk on them. I'm guessing it's the sugars in the Crest. Also, probably the reason they mentioned trouble re-priming the wick at the beginning of this thread was that the Crest had gunked up the wick. It would be hard to see with the naked eye as it is light colored. The Crest ProHealth ("alcohol-free") blue colored mouthwash, unfortunately, didn't even faze the hardened gunk on my m4xx series atomizers even after 3 days and looks like it actually added its own light coating of gunk. I've never seen anything here about anyone actually inspecting the coils under magnification to tell if the method actually did anything to the gunk.
Maybe VG based liquid might get cleaned off better - dunno. I figure that the problem isn't glycerin or glycol but that it is the sugars in sweet-ish e-liquids that is the culprit here. As to the claim being just to clean the air passages, well I reckon that might be true but hot water and blowing them out will do the same thing cheaper/faster. I was just hoping that someone had - at long last - discovered a convenient way to get the hardened/carmellized coating off of the coils and was pretty bummed after being so jazzed about the possibility this might work. This is the thing that prevents a decent hit on a vaporette more than anything else because it insulates the wire from the juice with a commensurate temperature drop between the coil and liquid. Makes you drag longer/harder and finally burn the atty out.
All this said, the only thing I've found that gets an atty coil perfectly clean is to heat up one end where the coil is soldered or crimped to the wires that go down to the connector with a soldering iron and a little rosin flux, then flush with a syringe of alcohol. The gunk liquifies and just bubbles right off of the coil wire and out of the fibrous whatever that it is wound around. The alcohol flushes away the re-liquified gunk and, at the same time, dissolves and removes the flux as well.
Of course, this is a real p.i.t.a. and I only do it when I have to repair an atty that has either had the wire break at the connector center pin or that they didn't attach the coil to the wires well and it burned there due to the high-resistance connection generating way too much heat or it just worked loose. I either just re-solder the connection or take off one turn and re-solder the end of the coil back to the wire - makes for a really nice about 2.0 to 2.2 ohm m4xx atty that nokes like a freight train. Hope some day somebody finds an easier way to clean these darn things...
Rick