The article linked is a good read, check it out. It doesnt go into "the best" way, because that is a matter of opinion, and a debate that often gets heated. If you want my opinion, a quick blow to the skull with a large heavy object. Some will disagree with me, and that again is thier opinion. As for flushing, the odds of it surviving and making it to the wild are slim to none, but if it does, and it introduces a disease into a native population, you will feel oh so bad about it.