An extremely controversial subject I have found, due to the evil spirits left from partial combustion. No recommendations, but here is what I do.
I clean my glass pipes in an alcohol vat, and I save the liquid. I also save all my pipe cleanings, roaches, etc in a jar. When the jar gets full, I dump in a quart jar along with the alcohol from cleaning my pipe. I shake that every time I think about for the next day or so, and then decant through a fine metal filter and a couple coffee filters.
I then mix that with water and equal parts hexane and shake again, decanting into a separatory funnel and letting it settle into layers.
Once it has settled out, the water, alcohol, sludge, and evil spirits will be on bottom, and the polar hexane with the cannabinoids that it stole from the non polar alcohol will be on top.
I bleed off the ugly stuff from the bottom, and pass the hexane through a .45 micron syringe filter to remove the fine carbon particles which have absorbed evil spirits and taste, evaporate off the hexane, and voile, reclaimed cannabis oil.
Since the lighter lower boiling point constitutes have been disproportionately boiled off in the original smoking or vaporizing, the resulting oil will be high in pain relief and sedation, but lower in euphoric high.
I will come back and attach process pictures and ones of the clean bright oil once I have been around long enough to do so.
GW