65 ILCS 5/11-38-3

All plumbers or other persons interested in the plumbing work, after the completion of the plumbing work, and before any plumbing work is covered up in such a building, or on the premises connected with such a building, shall notify in writing the examining board or officer that the building, or the premises, are now ready for inspection. It is unlawful for any plumber or other person to cover up, or in any way conceal any plumbing work in or about such a building or premises until the examining board or officer approves of the plumbing work.