I was told clove oil is the best. If god forbid I had to put a fish out thats what I would do. Also (not quite sure how humane) Ive heard putting him into a bowl then overdosing on alkaseltzer (typos) or Ice but that to me seems bad. Id go with clove oil if you HAVE to put him out.

That sucks. Don't beat yourself up over it, these things happen.