Place roast into a slow cooker and rub dressing mix over top. Pour water around roast. Cover and cook on High until meat is tender and can be easily pulled apart with a fork, 5 to 6 hours.

Remove meat and shred with two forks. Return meat to the slow cooker; add pepperoncini and as much pepperoncini juice as you like for additional flavor. Cover and cook for 1 more hour.

Serve on buns.