PBT – flexible (usually gray or black) plastic pipe which is attached to barbed fittings and secured in place with a copper crimp ring. The primary manufacturer of PBT tubing and fittings was driven into bankruptcy by a class-action lawsuit over failures of this system. However, PB and PBT tubing has since returned to the market and codes, typically first for "exposed locations" such as risers.
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 when the sewage is splashed during the repair. The plumbers skin during the repair does come into contact with the sewage water. The owner of the toilet might not report to the plumber they have already tried Drano a highly caustic base .