Moving to Washington as a master plumber: every state's rule
Washington does not issue a statewide master plumber license, so there is no reciprocity to speak of. Here is what that means in practice.
Washington master plumber
No individual license at this level
Issued by Washington State Department of Labor & Industries, Plumber Certification Program
Washington has no master plumber license. WAC 296-400A-010 lists every certificate the state issues (journey level PL01, residential PL02, residential service PL04, pump and irrigation PL03, domestic well PL03A, backflow PL30, and trainee), and the Journey Level Plumber certificate is the highest credential an individual can hold; the only add-on is the Medical Gas Piping Installer endorsement (MG01), which is a specialty, not a supervisory tier. Since July 1, 2021 a business that advertises, bids or performs plumbing work must hold a Plumbing Contractor license under RCW 18.106.400, but that is a business registration rather than a person-held trade license: the firm registers with the Department of Revenue, files a $6,000 surety bond, carries $250,000 combined (or $200,000/$50,000) liability insurance, pays a $148.10 license fee plus $53.20 to designate a Washington-certified plumber who works for the firm full time, and renews every two years; no exam is taken by the owner. An out-of-state master plumber therefore has nothing to transfer to at this level. To work as a plumber they obtain the journey level (PL01) certificate through the journeyman path (Idaho reciprocity or license review plus the Washington exam), and to contract they form a business and license it as a plumbing contractor with themselves or an employee as the designated certified plumber.