The hard part is getting the tire on, because the carbon bead is so tight. The soap and water is just to make sure the bead is seated all the way around when you inflate. But that's done already, putting in the sealant is easy. If you do it yourself, just remove the valve core, pour in an ounce of sealant, replace the core, and inflate. Hang up the bike while you do it so the weight of the bike doesn't break the seal of the tire. Especially living in New York, I'd use sealant. It's the best set-up for city riding.
Alex