A common task for a plumber is to diagnose a broken sewer/waterline, pinpoint where it needs to be dug up, safely excavate that section of piping, and make a repair.
There are many different ways to repair broken lines these days, but if the line is completely broken, many times the only repair option is to dig it up and complete a spot repair. If you are a small plumbing shop, and you sub out the excavation to another contractor, this information will fall on deaf ears. But if you would rather get paid full price for the excavation aspect of
