This is it:
http://forum.grasscity.com/harvesting-processing/417811-propylene-glycol-thc-tincture-recipe-me.html
I dont like this method because he isnt really blending the thc with the PG he is boiling it into it (trying to take a round peg and stick it in a square hole basically.. with enough force its gonna work but there is gonna be gaps)
Now as far as a further explaination of the extraction method, ill tell you my thoughts on the extraction using good old buetain. First off you can google "honey bee extractor" and get one of those or you can follow my method.
Take you an MnM minis tube and drill three small holes in the bottom of it (I like to use the small point of a nail, holes down need to be large you dont want anything falling through them!)
Then poke a small hole in the top for the tip of the can (again I like to use the pointed end of a nail, and just kind of work it gently until you get something that the nipple of the can can go into pretty good)
After that, take about an ounce of some green, and remove all seeds from it, leaves stems and everything else REMOVE ALL SEEDS ALLL SEEDS one more time ALLLLLLLLLLL SEEDS, the oils in the seeds cause problems, give you headaches, and make you shoot blanks. There is nothing in seeds of any value besides baby plants, and I dont grow so baby plants are useless to me.
now take you an eletric coffee grinder, and run your ounce through it, you should litterally have a powder so fine you could snort it... dont snort it.. that would be dumb... and painful.. and useless.. trust me voice of experience here...
Take this powder and pack it loosely into your MnM tube, you want to try and get as much as you can in there. Pack it good but leave room for air.
Now take a glass cooking pan, and set it inside of a shallow bowl of warm water, you dont want water in the pan, just around it.
Hold your MnM tube over the pan and run about two cans of buetain through it, after you have done that you can empty the tube and pack more and run another two cans through it, Normally I end up having to do an ounce in a bout three payloads, so six cans of beutian.
After that just leave it alone for about an hour and a half.. it normally takes less time but I would rather you be safe then sorry.. So in about 1 to 1.5 hours come back, and there will be an oily honey like stuff that is around the color of reeses PB.
Take you a razor blade.. a razor blade... not a credit card.. or a spoon.. or anything else that you think might work in place of a razor blade.. trust me.. I have tried everything and I mean everything! and scrape the stuff into a pile, generally you will get about 3-6 grams of pure THC out of an ounce of your normal street type bud.. If you use something like dro or really high grade stuff, I have gotten up to 12 grams (which is almost 50% THC content, thats really really good)
Now you can vape this stuff straight out of a normal vaperizer, if you use your ecig it will most likely gum up the atomizer, in this form, what ever you do dont smoke this stuff in any way that uses a lighter directly to the extract, it will all burn up before you even start hitting it.
Now the great thing about THC and most active chems in plants is that its a non-polar meaning that it will litterally mix homogeneously (very very well blended) with any other non polar liquid, most of which are your clear alcohols in nature. Rubbing alcohol is commonly used because it drys very quickly, but I prefer vodka cause if you injest it, its ok. Strength is not an issue at all, we have already done the extract so all we are looking is for a method to suspend the extract to keep it from degrading under sunlight (THC litterally will rust if left exposed to the air, so we have to suspend it in something)
Take an eye dropper and drip vodka on it, recycling your drops.. it should take a couple shots or so using this method to get it all soaked up. The color will be a greenish black.
Afterwards your safe to store it like this in a freezer for as long as you need to, you can drop it in your ecig cards this way, or another vaporizor, a word to the wise, is give it about 10 mins to dry before putting heat to it, so that its not so harsh.. smoking vodka is harsh lol, so let the vodka dry a bit first...
I have also taken the time to suspend this is PG using my method above, I really wouldnt advice it, generally its just to much trouble for what its worth, the only thing it adds is simply adds a bit more smoke and maybe flavoring.. Personally I dont think its worth the trouble, it dosnt help save your atomizor really all that much.... just drop the vodka based stuff on it and smoke it that way, when your done clean your atom real good with rubbing aclohole and you will be fine!
Some other fun stuff to do with your new found thc juice, is to just put a couple drops in your mouth under your tongue, it stings a little at first but about 30 mins later you will wonder how the heck you got so high lol!