Washington Facts about State Certification for Plumbers: Washington state requires a state certification for plumbers who wish to work in the state. This certification is given out by the Department of Labor & Industries (L&I). The certification process involves passing an exam, meeting experience requirements, and completing a background check. Types of Washington Facts about State Certification for Plumbers: 1. Exam Requirements: All applicants must pass a two-part exam administered by the Washington State Department of Licensing. The exam consists of a trade-specific knowledge portion and a business and law portion. 2. Experience Requirements: Applicants must have at least four years of experience as a journeyman plumber in Washington state. 3. Background Check: All applicants must complete a background check to ensure they meet the standards for a state plumbing certification. The background check will include a criminal record check and a financial check. 4. License Renewal: Plumbing certifications must be renewed every three years. Renewal requires completion of continuing education courses.