Plumbing Apprentice Year 3: Course C; This is one of four 8-week courses that comprise the Year 3 Plumbing Apprentice training. This is offered by Hyflex for large groups and Online for smaller groups. Year 3 of the Plumbing Apprentice training covers commercial plumbing, advanced gas piping and flue venting, indirect waste installations, plumbing repairs, and pipe sizing in larger buildings.