Google it people! according to google, if i spend around $800 for all the laboratory glassware and what not, for vacuum distillation, and i grind herb (or shake or trim) very fine and mix with D-Limonene which has a higher boiling point than THC. put this slurry into a 5000ml boiling flask, and under correct vacuum and heat, you can literally boil out nearly all the THC out of this slurry and recondense it in another vile. The ending result should be SUPER PURE Hash oil! and next to no THC will be thrown away because you can just boil it all out until no more will collect.