How to Repair Drain Lines Under a House


Nearly all residential drain lines these days are plastic and much easier to repair than metal. According to one licensed plumbing contractor of nearly 30 years, "If you have an older home which still uses metal drain pipes, you may be better off to replace, rather than repair them since metal pipes typically leak due to rust from age." Once leaking begins in one spot, the likelihood of damage throughout the drain system is high.

Things You'll Need

  • Hacksaw
  • Measuring tape
  • Pencil
  • 10-foot length of drain pvc pipe with diameter corresponding to the pipe being repaired
  • 2 drain pvc couplings with diameter corresponding to the pipe being repaired
  • 1 can pvc and cpvc purple primer
  • 1 can pvc medium clear
  • Identify the location of the damage by having your assistant fill the tubs and sinks in the house with water while you gain access under the house. While you scan the pipes, have your assistant release all the water. Check for leaks, and mark the locations on the pipes with a pencil. Have your assistant turn off the water and allow two to three minutes for it to drain.

  • Cut out the damaged segment of pipe using the hacksaw. Cut back two to three inches on each side of the damage to ensure a damage- free connection.

  • Measure the length of the damaged section and cut a replacement section from the 10-foot length of pipe. It should measure about half an inch less than the damaged section. This will provide flex room to install the couplings on both ends and still be able to attach the new section to the existing pipe.

  • Swab all the connections with the pvc purple primer to clean and soften the plastic and make bonding easier. Completely swab the inside of the bell for each end of both couplings. Swab two to three inches up the ends of both the replacement pipe and the existing pipe.

  • Swab over the primer inside the couplings and over the ends of the replacement pipe with the pvc cement. Insert the ends of the replacement pipe into the couplings and bump them against something solid, such as the foundation, to ensure proper seating.

  • Swab over the ends of the existing pipe and the inside of the couplings. On the end you will install last, use a copious amount of glue to allow maneuvering time since it will likely be a tight fit. Fit the replacement section with couplings on each end of the existing pipe.

  • Wait approximately five minutes for the pvc cement to dry, and have your assistant fill the tubs and sinks with water. Have your assistant release all the water while you check the replacement section of pipe for leaks.

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  • Wayne Roughton; Licensed Plumber; Columbia, NC
  • Photo Credit coude en pvc de 45° image by Marie-Thérèse GUIHAL from
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