What affect does the pipe pitch of drain lines in a home or commercial building have with regards to a possible backup?

Pipe pitch maybe one of the most important concepts in plumbing. It’s where the phrase “shit goes down and stink goes up” originates from. Waste water is supposed to drain away from the fixture it serves. Did you know that DWV (Drainage, Waste and Vent) fittings have pitch already built into the fittings. This means when you put pipe together with drainage fittings the piping will never be completely straight. It will always have some pitch to it.

 

  • Having the correct pitch is paramount when installing plumbing drain lines. Most people think that having more pitch is better for
    Picture of Pipe Pitch

    Pipe Pitch Examples

    a sewer drain line, this is not the case. Think about how water would flow with suspended solids. There is a point where too much pitch can actually be the cause of back-ups. The general rule of thumb is a ¼” per foot of pitch. As you steepen the pitch the velocity of the water increases, if the pitch is too steep the water may begin to pass up the suspended solids leaving them behind. If the solids continue to be left behind you’ll have a full blown sewer back-up. Remember this “a lazy sewer is a good sewer”. You’re better off putting less pitch on the pipe so the solids remain in suspension moving slowly along and eventually discharging into the municipal sewer.

 

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