I use a short cleaning rod with a bronze brush of what ever size gauge and carb/brake cleaner. I remove choke and spray with carb cleaner and vigorously scrub inside. Then let cleaner evaporate and reinstall. It seems to work for me and the carb/brake cleaner really strips the plastic out. I run a bore snake thru gun after every round when sighting in and usually scrub the choke as mentioned above after no more than 5 rounds.
Ridge Rooster