First off, if no culture was done, its time to find a different vet. Second, baytril isn't the only antibiotic. Another common one used on snakes is Fortaz. And without doing a culture, you have no idea if its bacterial, fungal or virus. I would never euthanize an animal unless it was a terminal illness. Also RIs can take a while to kick. And if it got better, than came back, you probably have a husbandry issue. Most reptiles can kick slight bacterial RI on their own with proper husbandry. Bump the temps up to put their own immune system into overdrive and you should have temps bumped anyways while using antibiotics. If you are set on euthanizing, then a vet is going to be the best way. They can do it painlessly. But personally, I feel if you are willing to give up on an animal over something like an RI which is fairly common as a reptile ailment, then you really need to rethink if breeding is something for you as I'm pretty sure, this wont be the last time in your lifetime you will encounter a sick pet. Or actually I just thought, if you are really ready to give up, then put him in the local craigslist or talk to your local herp club and tell em you got a X type of ball python with an RI and you cant afford to care for it anymore and are just giving it up for free to someone who wants and can care for it. Better than sentencing the animal to death for a perfectly curable illness.