How to Install a Backflow Preventer Sewage

Written by steve sloane
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How to Install a Backflow Preventer Sewage
Cut though the main sewer line using a handsaw. (handsaw image by AGphotographer from

When there is a blockage in a main sewer line, the sewage can back up and travel up through the sewer pipe and into the various household water fixture drains. To stop this, a backflow valve is installed in the main sewer line. This valve has a hinge flap that opens when sewer waste passes through it but closes if the waste travels back the other way. The main sewer pipeline is cut, and the valve is primed and cemented into place.

Skill level:

Things you need

  • Tape measure
  • Marker pen
  • Handsaw
  • Workman's knife
  • Damp rag
  • PVC primer
  • PVC cement

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  1. 1

    Measure the length of the backflow valve's body, not counting the inlets on each end of the valve where the sewer pipes will be installed. Locate the position on the home's main sewer line where the backflow valve will be installed, and make two marks on the pipe the same distance apart as the length of the valve body.

  2. 2

    Cut through the main sewer line at both marks with a handsaw (the cuts will be straight and parallel with each other). Scrape away any burrs from the cut pipe ends with a workman's knife, and wipe the outside ends of the pipe cuts with a damp rag.

  3. 3

    Brush PVC primer around both outside pipe ends to a depth of 2 inches. Apply primer the inside ends of the backflow valve. Brush on PVC cement to all four primed areas. Quickly push the sewer pipe ends into the ends of the backflow valve, making sure the hinge flap faces the direction that the sewer waste will travel (the hinge on the flap will also face up). Hold the sewer pipes to the valve for 10 seconds while the cement dries.

Tips and warnings

  • If room permits, a circular saw can be used to cut through the main sewer line.
  • Wear eye protection when cutting through the sewer line.

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