Mich. Comp. Laws § 339.6101

Sec. 1101. As used in this article: (a) "Apprentice plumber" means an individual who is registered under this article as an apprentice. (b) "Board" means the state plumbing board described in section 1105. (c) "Building sewer" means that part of the drainage system that extends from the end of the building drain and conveys its discharge to a public sewer, private sewer, individual sewage disposal system, or other point of disposal. (d) "Domestic water treatment and filtering equipment" means residential water treatment and filtering equipment used in 1-family and 2-family dwellings. (e) "Journey plumber" means an individual, other than a plumbing contractor or master plumber, who is qualified to engage in the practical installation of plumbing and who is licensed as a journey plumber.