I am trying to understand what type of PVC pipe is required for the main septic drain line from the house to septic tank.

The IRC says this:

International Private Sewage Disposal Code 2012

Chapter 5 - Materials

Section 505 - Pipe , Joints and Connections

505.1 Pipe. Pipe for private sewage disposal systems shall have a smooth wall and conform to one of the standards listed in Table 505.1.

Table 505.1

I see SCH 40 PVC is acceptable, but what about the thin wall sewer/drain pipes?

I am wanting to know specifically how thick the pipe wall must be, or is this simply a consideration based on the location of the pipe - i.e. traffic areas vs no traffic, tree roots, etc)


This is a thin wall pipe

This is a Sch 40 thick wall pipe

Specifically, this item in the IRC has me confused:

Coextruded composite PVC sewer and drain DR-PS in PS35, PS50, PS100, PS140 and PS200

Does that include the thin-wall sewer pipe listed above?

3 Answers 3


This is the wrong place to save a few bucks on the pipe - you may live to regret (and smell) it.

SDR 35 (not what you linked to) may (IIRC) be considered acceptable, but it's foolish to use it on the inlet side .vs. schedule 40. Likewise, you may only be required to use 3" pipe, but 4" is well-worth the minor cost increment in the lack of trouble it will assure you of for the relatively short run from the house into the tank. If you are using a PVC Tee inlet baffle rather than a cast-in-place baffle, that should be a 6x4X6 tee with appropriate 6" pipe extension for the lower leg. It's acceptable to exceed requirements, and doing so can save trouble later on.

A lot of the other pipe is only acceptable for the drain-feild side of the system, distributing the treated wastewater. In my opinion and my septic system, it's schedule 40 all the way to the distribution box (beyond the tank outlet.) Cheesy pipe can be used in the drainfield.


I don't have an explanation why one pipe is used over the other, but in all my days of running jobs, Sch 40 pipe is the only pipe used, no other kind of PVC. Cast iron is code too, but your question was not including that. I only mentioned it because that is the only other accepted material.

  • So the thin-wall pipe referenced above would not be suitable? May 22, 2014 at 3:35
  • 1
    In my expectations the inspector would flat out reject it. In my experience/concerns, I would not use thin wall regardless of its specifications. The Sch 40 I refer to will not crush like thin wall PVC. It for me is a peace of mind thing for such a critical part of a home.
    – Jack
    May 22, 2014 at 22:15

Schedule 40 all the way.

Is there a fitting to to connect the house 3" PVC to the distribution box hole? Since it has a tapered concave opening that starts at 6" and reduces to 4" (?).

Also, in agreement that this is no place to spare the change, are you recommending a 4" T connection for later practical purposes?

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