How to Replace Sewer Line in the Basement Floor?


Aided by gravity, house drains all slope downward, eventually joining the main sewer line and exiting the house. The lower the level of the main sewer line, the more options the homeowner has for installing plumbing fixtures, such as basement bathrooms or wet bars. Unfortunately, when a buried sewer line must be replaced, which can happen if it has an inadequate slope or if it breaks due to soil shifting, it's a major project. Replacing the line isn’t complicated, but removing the concrete and the old pipe is messy and labor intensive.

Things You'll Need

  • Concrete saw
  • Electric jackhammer
  • Shovel
  • Pipe saw
  • Cast iron pipe cutter (optional)
  • 4-inch PVC pipe
  • 4-inch PVC sweep elbow
  • 4-inch PVC couplings
  • Sledgehammer (optional)
  • Two, 4-inch sewer line rubber couplings (optional)
  • Screwdriver (optional)
  • PVC primer
  • PVC glue
  • Turn off the water supply to the house and instruct residents not to flush the toilets.

  • Locate the buried sewer line using the spot where the line enters the basement floor as the first reference point. Go outside, find the sewer clean-out, which is usually within a few feet of the foundation, and use that as the second reference point. In most cases, the main sewer line will be in a straight line between these two points.

  • Cut two lines with a concrete saw in the basement floor to form a 1-foot wide trench over the buried sewer line.

  • Break out the concrete between the two cut lines with an electric jackhammer and remove the concrete bits and debris from the trench. Only sand or soil should now be beneath.

  • Dig with a shovel to unearth the sewer line. The line will be nearest the surface where the pipe enters the basement floor and slopes downward toward the exterior wall.

  • Cut the pipe 4 inches away from the exterior wall. If the sewer line is PVC, you can use a pipe saw, but if it’s cast iron, a cast iron pipe cutter is necessary. Unless you’re very familiar with cutting cast iron, this step should be performed by a plumber to reduce the risk of shattering the section of pipe that runs through the concrete wall.

  • Cut the other end of the sewer pipe above the floor where you want to attach the new line.

  • Remove the old section of pipe. If the pipe is cast iron, breaking it into smaller pieces with a sledgehammer will make it easier to get out.

  • Measure, cut and install a new 4-inch PVC sewer pipe, making sure the pipe drops at the rate of 1/4 inch per 1 foot. This is the standard slope for waste drainage pipes.

  • Connect the new PVC pipe to a cut PVC pipe, using 4-inch PVC couplings and applying PVC primer and glue in the connections as specified on the products’ package.

  • Install a 4-inch sewer line rubber coupling between a new PVC pipe and an old cast iron pipe. This type of coupling has a rubber boot that the ends of both pipes slip into, and metal bands around the outside of the rubber. Once the pipes are in place, locate the screws on the bands and tighten them with a screwdriver to seal the connection.

  • Install a 4-inch PVC elbow sweep fitting where the new sewer pipe will come out of the concrete floor and connect to the old vertical drain line.

  • Attach a new section of 4-inch PVC pipe to the old vertical drain line and also to the PVC elbow sweep fitting, using the PVC primer and glue as directed. If the old vertical line is cast iron, use another rubber sewer coupling to connect the PVC pipe to the cast iron pipe.

  • Fill around the new pipe in the trench with sand, packing it under the pipe first and then around the sides and top. The sand level should reach the bottom edge of the existing concrete floor.

  • Fill the trench with sack-type concrete, mixing it with water as directed on the package and smoothing the wet concrete level with the existing floor and around the new pipe where it exits the floor.

Tips & Warnings

  • Wear protective eyewear, leather gloves, long sleeves and long pants when sawing and breaking out old concrete.
  • Once you cut the old sewer line, sewer gases can seep into the basement. Keep a basement window open for ventilation.
  • Operating an electric jackhammer requires physical strength. Take breaks to keep from overtaxing your arm, shoulder, neck and back muscles.
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