Can I use a spigot / dispensing spout on the 5-gallon carboy?

Yes, the hole in the center of the cap is designed to work with commonly available 2” threaded spigots / spouts. To use: 1) Remove existing cap, 2) replace with the 2" spigot cap, 3) make sure spigot is in the off position, 4) turn the carboy on its side so the spigot points down and check to make sure the spigot isn’t leaking. Spigots are available at distributors, like at https://www.grainger.com/product/DYNALON-Faucet-Includes-Closure-3UDG9.