How to Replace Home Sewer Lines

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The sewer line as we know it today was developed around 1850, and it is essential for removing waste and waste water from your home. The sewer line begins 5 feet outside the foundation of the home and is made of clay or ABS plastic. It is the clay sewer lines that are most often in need of replacement because they are easily broken by tree roots or by the movement of the ground. A broken or damaged sewer line will cause raw sewage to back up into your home, producing a smelly and unsanitary mess. It is often a backup that alerts you to a problem in the sewer line, but replacing the sewer line will help prevent any future backups. The general steps for replacing a sewer line are the same regardless of what they are made of.

Things You'll Need

  • Shovel
  • Shoring material
  • Pipe
  • Fittings
  • ABS couplings
  • One or two flexible couplings
  • T-handle torque wrench
  • ABS primer and glue
  • Measuring tape
  • Permits
  • Helper
  • Soil pipe cutter
  • ABS saw
  • Tamper
  • Test plug
  • Bicycle pump or air tank and hose

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Request copies of the planning commission map showing where the municipal sewer is located and at what depth your home's sewer line connects to it. The map will also show the approximate length of your sewer line and its approximate location. You need this information to locate the sewer line on your property.

Secure a permit for the job. Not having a permit may result in fines and you will be required to stop all work until a permit is obtained.

Call a line location company to come out and mark the location of the utility lines in the ground before you start digging. You may get the contact information through a utility company or often there are advertisements posted at the planning commission office.

Locating the Sewer Line

Mark the sewer lines approximate location nearest the street by using the information from the planning commission map. The map is not always correct as builders often make changes during construction; however, most sewer lines are withing a few feet of the location marked on the map. The information on the map will allow you to determine the approximate length and depth of the trench you will be digging and the possible location of where the sewer line may be coming from your house. Use the information in the next few steps to locate the sewer line near your house.

Locate the sewer line if your home is on a slab. Find the toilet nearest the side of the house where you placed the marker at the street or property line; then, visualize where the sewer line may be coming out of the house in relation to the marker. Use a metal probe and a shovel to probe the ground for the sewer. Do not use a lot of force when pushing the probe into the ground as you may break the sewer pipe. When you locate the sewer it should feel like you are hitting a rock.

Locate the sewer line if your home is on a raised foundation and no clean-out is visible. Go under the house and locate the large pipe to which all the other drain lines are connected; then, follow the pipe to the foundation wall. Measure the distance from the nearest vent or crawl space opening and use that measurement on the outside of the house to locate the sewer.

Exposing and Removing the Old Sewer Line

Expose the sewer line starting nearest the house and work your way toward the street using the existing sewer line as your guide. Be sure to expose the entire sewer line.

Install the shoring in the trench if necessary to prevent cave-ins. If you are unsure of how to shore up the trench or if you need to use shoring, see the regulations published by OSHA. The general interpretation of the regulation is that if the trench is less then 5 feet deep and the ground is stable as determined by a competent person, you do not need to shore up the trench. Most sewer lines are 2 to 4 feet deep just outside the home's foundation, which means that it is highly unlikely that your trench will be less than 5 feet deep.

Dig out all the way around the sewer line at both ends. You should be able to stick your hand under the sewer line and reach out the other side on each end.

Cut the old sewer line out. Wrap the chain of the soil pipe cutters around the sewer line at one end beyond a joint and cut the pipe; then, cut the opposite end of the sewer line. If the pipe coming from under the house is cast iron, be extremely careful while cutting it. Old cast iron is fragile and trying to cut it too fast may cause a running crack in the pipe. If this happens you will have to replace most, if not all, the cast iron pipe under your house. The best advice is to tighten the soil pipe cutter slowly--you will hear the pipe snap when it is cut. After the cut, be sure to inspect the pipe carefully to ensure no cracks have developed. If the pipe coming from under your house is ABS plastic, then use a T-handled torque wrench to loosen the bands and remove the coupling.

Determine the fittings and pipe needed to replace the sewer line. With the line exposed you can see what type of pipe comes out from under the house and be able to measure how much pipe will be needed. You will need to include two wyes, female adapters and two plugs. These are needed to install a test fixture near the street and a clean-out near the house. Remember that you will need enough pipe to replace the old sewer line as well as make additional connections to the wyes. If the pipe coming from under your house is cast iron you will need a cast iron to ABS coupling to attach the two pipes together. If the pipe coming from under your house is ABS you will need an ABS coupling to connect the two pipes together. If the pipe coming from under your house is copper, remove it and replace it with ABS. Be sure to include one clay to ABS coupling so that you can make the connection to the clay pipe coming from the municipal sewer.

Remove all the old sewer line from the trench being careful not to break it. You cannot leave debris or broken sewer line in the trench. If debris is left in the trench the inspector will fail the job and you will have to clean out the trench and reschedule the inspection. Leaving broken sewer line in the trench may also result in damage to the new sewer line.

Smooth the bottom of the trench with a shovel and ensure that you have a grade of 1/4 inch per foot fall. Place a level in the bottom of the trench and check the bubble inside the level. A quarter of a bubble should be beyond the line closest to the house. A 1/4 inch per foot fall means that for every foot of travel toward the street or property line the pipe should be 1/4 of an inch lower.

Install the New Sewer Line

Install a coupling on the pipe coming from under the house. Remember that the type of pipe coming from under the house determines which coupling you will need to use.

Cut a piece of ABS pipe about 5 to 6 inches long using an ABS saw and remove any burs; then, install the pipe into the coupling.

Position a wye so the bend is facing up and the sweep of the bend is going toward the street. This wye is for the clean-out and will prevent waste water from any future backups from coming up in the house.

Glue the wye to the opposite end of the pipe installed in the coupling. Be sure to apply primer and glue to both the inside of the wye and the outside of the pipe. Twist the wye from side to side while pushing the two pieces together to spread the glue.

Dry fit one full length of pipe into the opposite end of the wye and lay it in the trench. Then continue to dry fit couplings and pipe until you reach the end of the trench. Let the last length of pipe extend at least to the pipe coming from the street. Do not attempt to dry fit the end of this pipe to anything. Instead, lay it to the side of the trench for now.

Install a clay to ABS coupling onto the pipe coming from the street; then, cut and install a short piece of pipe just like you did near the house.

Position a wye so the bend is facing up and the sweep of the bend is going toward the house. This wye is for the test fixture.

Glue the wye to the opposite end of the pipe installed in the coupling. Be sure to apply primer and glue to both the inside of the wye and the outside of the pipe. Twist the wye from side to side while pushing the two pieces together to spread the glue.

Bring the last section of pipe near the wye you just installed; then, mark and cut the pipe so it will fit into the wye.

Place the level on the new sewer line in several locations to check that you still have a 1/4 inch per foot fall. If the fall is less then 1/4, move the pipe out of the way and remove dirt until you get at least a 1/4 per foot fall. The fall can be greater then 1/4 inch per foot but not less.

Starting at the house, prime and glue each of the pieces together remembering to twist each piece a quarter of a turn to spread the glue as you are pressing them together.

Install the Vertical Pipes in the Wyes

On the clean-out wye, measure and cut a piece of pipe long enough so the end will be above ground level.

Glue a female adapter onto one end of the pipe and glue the opposite end into the top of the wye. Then install a plug in the female adapter.

On the test fixture wye repeat the same process, except that the vertical pipe does not have to extend above ground level. The shorter this pipe is the better.


Attach an air hose or bicycle pump to the hose on the test plug.

Remove the plug from the test fixture and insert a test plug into the pipe just beyond the sweep of the wye. Generally the test plugs are about 3 to 4 inches long and are flexible so there should be no problem with getting most of the plug past the bend.

Fill the test plug with air to form a watertight seal inside the pipe. Some test plugs have a pressure gauge on the air hose so that you cannot overinflate the plug. You can further test the seal by letting water run into the pipe; if you see water getting past the plug then inflate the plug until it stops.

Fill the pipe with water until it is visible in the vertical pipe of the clean-out. For inspection purposes the water level must remain steady for at least 30 minutes. It is always a good idea to fill the line the day before the inspection, then arrive before the inspector is due to check the water level yourself. As long as there is no drastic change in the water level it should pass inspection. The inspector will also place a level on the new sewer line to check for the proper fall.

Get the signed inspection from the inspector once you pass. If you did not pass, he will give you a list of the things that must be fixed. Repair those items and schedule a new inspection.

Finishing the Job

Remove all the shoring from the trench if necessary.

Back-fill the trench starting at the deepest point.

Tamp each layer of dirt firmly as you put it in the trench. You can do this by stomping on the ground as you add the dirt or rent a gas-powered tamper. Before using a gas-powered tamper make sure that there is at least 4 inches of dirt covering the pipe to prevent damaging the new sewer line.


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