Traditionally, sewer lines that need to be replaced are dug up using an excavator. An open trench is dug from the house all the way to the connection at the main line, the old pipe is taken out, and new pipe is installed. Then all of the dirt is backfilled into the trench, leaving a mound of dirt from the house to the main. With trenchless sewer replacement, an open trench is not required. A new pipe or liner replaces the original sewer with little or no excavation.