Pro Plumbers

Cast iron and ductile iron pipe was long a lower-cost alternative to copper, before the advent of durable plastic materials but special non-conductive fittings must be used where transitions are to be made to other metallic pipes, except for terminal fittings, in order to avoid corrosion owing to electrochemical reactions between dissimilar metals (see galvanic cell).[17]

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.
To unclog a bathtub drain the right way, you'll need to take the drain plate off. That's the little round plate that has the lever on it for opening and closing the pop-up drain stopper. It takes a little effort, but it's not too hard to remove and behind that plate, you have access to a straight drain pipe you can send the drain snake down. Check out the video above from This Old House for instructions.
Plumbers, pipefitters, and steamfitters may use many different materials and construction techniques, depending on the type of project. Residential water systems, for example, use copper, steel, and plastic pipe that one or two plumbers can install. Power plant water systems, by contrast, are made of large steel pipes that usually take a crew of pipefitters to install. Some workers install stainless steel pipes on dairy farms and in factories, mainly to prevent contamination.
The word "plumber" dates from the Roman Empire.[3] The Latin for lead is plumbum. Roman roofs used lead in conduits and drain pipes[4] and some were also covered with lead, lead was also used for piping and for making baths.[5] In medieval times anyone who worked with lead was referred to as a plumber as can be seen from an extract of workmen fixing a roof in Westminster Palace and were referred to as plumbers "To Gilbert de Westminster, plumber, working about the roof of the pantry of the little hall, covering it with lead, and about various defects in the roof of the little hall".[6] Thus a person with expertise in working with lead was first known as a Plumbarius which was later shortened to plumber.