I'm adding a 4th bathroom to my home and need to update the waste pipe going to the septic tank from 3" to 4". The pipe coming out of the foundation immediately transitions from 4" to 3" leaving < 1" of pipe between the foundation and the clean out fitting.

What would be the best way to cut off the 3" clean out so I can attach a 4" clean out fitting with such little room?

How much 4" pipe do I need to insert into a 4" fitting?

Pipe fitting

Pipe fitting 2

2 Answers 2


The bad news:

As already noted: you don't have enough pipe left inside the house to cut that clean out off and glue a new one one.

The good news:

It looks like they ran the 4" pipe through a 6" pipe sleeve, then packed it with (mortar?) to seal it. This means that instead of breaking up the foundation wall to replace the pipe, you "only" have to dig out the mortar inside the sleeve!

You'll have to:

  • Excavate on the outside down to the 4" drain
  • Open up enough of a trench that you can cut it off outside the wall, leaving enough exposed on the downstream side to put a new slip joint connector on
  • Cut off the clean out and 45° inside.
  • Remove all that mortar from inside the sleeve
  • Remove the section of 4" through the wall
  • Replace the 4" through the wall
  • Plumb in new waste lines as appropriate inside

Sorry, while it's simple it's not going to be easy...

  • I have a farmers porch right outside that pipe... What about using an 4" inside coupler? Do you think the little lip will block the sewage flow? pvcfittingsonline.com/…
    – Derek
    Oct 22, 2020 at 17:50
  • @Derek ooof... that's beyond my pay grade. I don't know if those meet code in general, but more particularly where you live. It would probably be a good idea to ask a whole new question about that, specifically, and indicate what jurisdiction you're in - code varies state-to-state (or country-by-country) and can even vary by city within a state.
    – FreeMan
    Oct 22, 2020 at 19:01

The unfortunate answer is, more than you have showing there. Do you see the shouldwr of the fitting? That's how long the pipe must be (roughly). You might be able to dig out the foundation seal to get more exposed pipe, but that then introduces a risk of that wall penetration leaking.

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