your post indicates you don't know how solvent extraction works. You aren't concentrating the thc, you're using a medium (solvent) which will attach to thc molecules that can be easily removed later. Butane is the most common solvent because it evaporates easily, CO2 is another. The idea is that the final product will only contain the chemicals the solvent can pick up and (if you do it right) it won't contain the solvent either.
Yeah its laughable how little cops know about Dabs. Our local ones just think its "that stuff you put in Vapes" so they freak out on every hipster they pull over. reminds me of that "this is called a 'roach'" scene in Fear & Loathing