Before you get involved with most plumbing projects, you'll need to shut off the water flowing to whatever you're working on. Most of the time, there are easy-to-access gate valves or compression valves that you can turn with your hand. Turn them clockwise all the way to turn off the water and counter-clockwise to turn it back on when you're done. For sinks, look under the sink and you'll usually see two valves—one for hot water and one for cold. On kitchen sinks, you might also see valves for the ice maker on your fridge or your dishwasher. Just turn them all off. For toilets, the valves are on the wall or right on the pipe behind the toilet.
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 .