How should I clean my gas key?

Awesome thanks

Pipe cleaners plus brake cleaning fluid.

FPNI    in white   to see when  its no longer dirty

I don't worry about cleaning the gas key or gas tube, it's a self cleaning system basically. All the junk will get blown out for the most part when shooting. Of course I clean everything else well ;)

This. I tried cleaning it with a Q-tip (bad idea) and got some cotton stuck. Would not recommend.

I got some soft bristle pipe cleaners at Brownell’s.

Pipe cleaners (not the arts and crafts type) and CLP.

GI manuals show using a worn bore brush to clean the gas key.
Insert it as far as possible by "screwing" and pushing it in, then rotate a few full turns to clean the key.

Another way is to soak the front end of the bolt carrier and key in a carbon remover like Slip 2000 Carbon Killer.
If you use a carbon killer, usually a pipe cleaner will remove whatever little carbon is left.

As the gas tube also... that part is "self cleaning". Meaning, the thousands of PSI of gas pressure run through it will blow out anything. Don't waste your time.

Yup

This.  Want to clean your gas key?  Shoot your rifle.

I've never once seen or heard of an ar not functioning because of a dirty gas key.  

I have seen people get all kinds of crap stuck in gas keys.

You don't need to worry about cleaning it. However, if it makes you more at ease to clean it, go to Harbor Freight and buy their small ultrasonic cleaner and put the BCG in there every once in a while and it will clean the whole thing real nice. Make sure you blow all the moisture out real good with an air nozzle.

I have one. It does not really do much more than make noise. Yesterday I cleaned 2 bolt carrier groups. After like 6 cycles with some "purple power" they were not clean. Wiping them with a rag and they were still making the rags black. Baked on carbon was not removedI have one more solution to try, Simple Green Pro HD. if this does not work then I will give the cleaner away.

Not so sure why everyone thinks the Harbor Freight cleaner is such a great device. I bought it because people were posting here how awesome it is. I tried cleaning brass with it. What a mess and it still did not come clean. I tried home brew brass cleaner and the Lyman stuff. I gave up trying to clean brass. Then I decided to use it for gun cleaning. I bought the Lyman gun cleaner for it and tried to clean my 1911. That was a huge fail. After 6 or 8 cycles the gun was still dirty and I ended up cleaning it the old fashioned way.

My last try was yesterday to clean AR15 bolt carrier groups. I disassembled them and tried this stuff called Purple Power. It did not work. I am going to try next time with Simple Green Pro HD.

I really would like to meet someone who thinks these things are more than noise makers. I want to see before and after results. I find it hard to believe I am the only one who has found them to be a waste of money. Yes I have tried both tap and distilled water. I heat it so I can barely stand to touch the liquid.

The gas key has a totally different purpose than the gas tube...that being said I periodically get that last sixteenth of an inch in the key with a pipe cleaner.

Q-tips FTW

Brownells sells a stainless brush made for cleaning the carrier key. The number is 749-000-648WS. It works great. It you go to the Brownells  site, then go to the Sinclair side of it, you'll find a lot of specialized cleaning tools for AR's.  

I have been shooting M16s/AR15s since 1992 and I don't recall ever cleaning the gas key and I have never had an armorer reject my rifle because the gas key was dirty.

Mine gets pretty filthy