CO2 works great. They don't get alarmed unless there is audible and/or visible commotion, so no spray usually. I have placed trapped skunk and trap (covered with old tarp) into a big lawn/leaf bag, then used a CO2 extinguisher. The noise may be unpleasant enough to agitate your trapped skunk. A smallish block of dry ice will generally do the same job. Avoid direct contact with the ice for both you and the skunk.
Drowning seems to be fairly easy when they have been trapped. I tie some paracord to the trap before baiting and setting, then fix up an Evel Knievel ramp leading just to the rim of a horse tank with deep-enough water. Pull the cord slowly and when the ramp quits, Senor Skunk and trap sink quickly in the water. Remove trap and skunk in an hour or two, empty the trap and dispose of the polecat. I have not been sprayed. yet
I'm interested in a humane kill, even for these pests, so a firearm is another choice when they are out and about and you are packing. Preferred armament for me is small gauge shotgun (think 20 gauge or smaller) but a small caliber belt gun can work fine. Wadcutters in my 32 S & W Long are very effective for head shots. A 22 short is also an easy way to head-shoot a trapped skunk. I have not been as pleased with the results when a non-trapped skunk is hit anywhere besides the CNS with a single slug, like from a 22. They seem to be a big target, but most of that is hair and a hit to the body often is not an immediately lethal wound, which can result in a spraying episode.
