Most states and localities require plumbers to be licensed. Although licensing requirements vary, most states and localities require workers to have 2 to 5 years of experience and to pass an exam that shows their knowledge of the trade and of local plumbing codes before they are permitted to work independently. In addition, most employers require plumbers to have a driver’s license.
Those who attempted to bring plumbing indoors faced technical as well as attitudinal challenges. Decisions on how wastewater was removed required as much concern as those made to ensure an adequate water supply. But equally vexing was the prevailing miasma theory of disease, which held that illnesses stemmed from "bad air" that was readily identifiable by its offensive odor. This led to a distrust of early indoor plumbing that tended to leak and a deadly fear of the sewer gas that accompanied the leaks. It is no wonder then that many individuals maintained a strong belief that elimination was best taken care of out of doors.