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]

plumbers must be asked directly what they charge hourly and if that is in addition to a service charge. The two are separate and I think they have gotten away with outrageous charges because of the potential of water damaging homeowner structures.   I had a plumber (not Home advisor) come and replace a part in my kitchen sink that was under warranty---the spray nozzle had been leaking...He charged me $85.00 for 15 minutes of work and I will never use Mr King again. 
When a person has a blockage in their sewage system they often try to fix it themselves by adding an acid or a base such as Drano in an attempt to dissolve or dislodge the problem. These chemicals can get into the plumbers eyes [14]when the sewage is splashed during the repair. The plumbers skin during the repair does come into contact with the sewage water.[15] The owner of the toilet might not report to the plumber they have already tried Drano a highly caustic base .