say you and your hypothetical friends purchase a large quantity of schwag. obviously, there will also be a large quantity of stems and seeds. what you could do is this:
collect all the stems and seeds into a container large enough to hold them.
pour 91% pure isopropyl rubbing alcohol into the container until there's just enough to cover all the plant matter. (MAKE SURE you use nothing of lower purity. the intent is to evaporate off the alcohol later, and using anything of a lower purity will result in unwanted chemicals remaining in the end product.)
let this mixture sit, agitating occasionally, for 24-48 hours. the alcohol should take on a green tint which will get progressively darker as more and more THC in the plant matter precipitates into the alcohol.
after this, strain out the plant matter and pour the alcohol onto a plate or tray deep enough to accomodate the volume of liquid. get out a hair dryer and start evaporating the alcohol.
this may take awhile, depending on how big the tray is (bigger is better) and how much alcohol you used. when you're positive that all the alcohol has been evaporated off, you'll be left with a gummy green residue which can be added back to your weed to increase it's potency. you can try extracting more THC out of the same plant matter by repeating the steps again.
disclaimer: i make no claims that this will not kill you or your friends. alcohol is flammable and should be treated with care. | 
