Hello,
I am wanting to convert an upstairs laundry room to a bathroom and moving the laundry to the garage. The original house has 2 bathrooms upstairs and 1 bathroom downstairs, total of 3, plus laundry conversion to a bathroom would result in 4 bathrooms. We were told that this requires a 4 inch sewer pipe. It is my understanding that the sewer outside the house is 4 inches, but 3 inches sewer pipe inside the house. If that is the case, is it possible to just connect to the clean out line? Or does it have to be 4 inches starting from the clean out pipe?? Not sure if I am even asking the question correctly. The common sewer line is under the driveway and would be very costly to break and re-do. Thanks in advance.

Hi Schun67...

In my area, if you have more than 3 toilets you need to increase the pipe to a 4" pipe. Sounds like it may be the same in your area... UGH!

Your best bet here would be to call a local plumbing inspector and ask him for confirmation... ;)

Let us know if you'd like to discuss more... OK?

Mark

Thank you for your reply. Will call the inspector, but I am wondering, does the entire pipe in the house have to be 4" or just the line going out from the house? Also, can a 4 inch pipe fit inside the outer wall?

You'd only have to bring the 4" pipe in to the point where it branched off for one of the bathrooms...could be the new bathroom or even an older bathroom. After you pick up one bathroom with the 4" you could reduce to 3" after that.

You would need a full-size 4" cleanout before transitioning to 3"...;)

In terms of 4" going up the wall... you shouldn't need to go 4" up the wall unless all 4 toilets/baths connect into that one pipe... hope that made sense.

Mark