Isopropyl alcohol does accumulative damage. Sam the Skunkman states he's tested more extractions than probably anyone. Not once, no matter how many times it was "washed or purged," has he ever had an iso extraction test negative for iso. Bleah.

Yeah, ethanol is great because I don't need to worry about the tiny residual alcohol in it. Not a bit.

Professional butane extraction companies re-distill large quantities of butane, for the sole purpose of removing mercaptans and other mystery oils. Significantly cleaner than most DIY extractors, I still prefer ethanol. lol To each their own. :D