I like to use a can of moisture free compressed air to blow it out from the threaded side of the 501. I just kind of hold the two together and blast it a couple times.
On the 801's I actually removed the guts from a battery, cut it in half leaving the threads along with about an inch of battery casing, then inserted a mouth piece into the new opening with the tube from the compressed air can forced into the mouthpiece hole. This makes a nice tight seal and when it's threaded to an atomizer it blows out everything. 501 can't do this but the canned air still works great for me.
-Bryce
I have considered doing this, but most of the canned air that I've seen contains a bitterant to keep people from huffing it. Wouldn't this leave a nasty taste on the atomizer? Or have you been able to find one without this "safeguard?"