My dad also used and swore by nicotine solution for black-fly and greenfly. He didn't boil it up, though. He just kept a large container of water into which he emptied his ashtrays and left the butts soaking. I would advise caution with this method. Nicotine is a poison, which is probably how it works. While smoking cigarettes over years causes problems associated with the body accumulating this poison, concentrating it in this way is probably inadvisable, in particular if used on fruit or veg.