Ive killed quite a few with the long stick (8 foot long, mine was an aluminum tube with a plug inside that was used as an injector) using acetone, but they were in foothold traps. I found it helps a lot if you can leave him for a few hours so he settles down a little bit, and talk gently to them as you are walking up to them. Stay low so they aren't as scared of you. Stay upwind. Let them smell the needle, they will get fiesty when they smell it and you may have to back up for a minute but the next time they won't care. Move back quickly after injecting them. I haven't done it in years but it worked well for me. Once in awhile there will be one that it just won't work with but I'd say about 80%-85% of mine I could inject with success. It was nice to have this option if you were close to houses, which was often my case.
I never drowned one in a live trap but Camofry gave you good advise.
I skinned mine before I removed the juice. I just cut way around the glands and never had a problem. Its amazing how they don't smell at all if they haven't sprayed in awhile. They are fairly docile animals and can't spray much past 8 feet (at least Ive never seen it that far)