I had (what i presumed to be) a failing wax ring on an upstairs causing a leak to the ceiling below. I cut a hole in the downstairs ceiling and confirmed water originating from the toilet drain pipe and only when flushed. I removed the toilet and am a little confused about what I'm seeing.

Are there flanges that seal on the OD of the drain pipe as shown in this photo? Is the gap between the brass plate (flange) at the very bottom and the cast iron drain a possible leak point? That gap was packed with wax when i took the toilet off.

A second issue is that I sheared the bolts when removing the top plate/repair flange I have pictured in my hand. They were phillips head so I assumed they would come out but perhaps they were set in the tile mortar bed.

Do I need to do anything to seal that gap I'm seeing around the edge of my drain pipe?

Whats the best approach for reattaching what I assume is this repair flange? Diamond bit to drill through the mortar bed and really long screws to grab the sub floor? Eopxy? Screw into the mortar bed itself?

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  • I'm not familiar with that flange design, but cast iron plumbing is mostly from before my professional time. I think I'd be considering cutting it off and attaching modern PVC or ABS parts with a no-hub clamp. I did that in one of my homes. What does it look like underneath?
    – isherwood
    Feb 21, 2023 at 23:15

1 Answer 1


Let's gather some dimensions/sizes first.

What is the inside diameter of the cast iron drain pipe, it looks like 3 inch or 4 inch (measure it). While you have the measurement tape in hands, also measure the distance from top of cast iron pipe to the top of the floor. You will need those dimensions to get correct size extender.

You have a extender installed (the red part) that now fits over the drain pipe. The reason is that the pipe end is way below the floor level. That is fine but heavily dependent on the quality of the seal between the extender and the pipe (which seams to be your problem (leaking). It will be stressed every time you flush.

There are extenders that fit inside the cast iron pipe, that are much less susceptible to leaks (only leak if there is a back up in the drain pipe) but not with flushing.

Armed with the measurement go to store and buy the right size extender.

Follow the instructions how to install it.

You might be able to leave the current one in place and just insert the new one.

  • 1
    Based on what I'm seeing and some discussion in other forums, I actually think the red thing is part of the toilet flange. It looks similar to this design: oatey.com/products/…
    – Timv
    Feb 23, 2023 at 4:10
  • Based on the saturation I'm seeing from underneath, and testing of that seal I don't think that gap shown is not whats leaking, it seems likely a failure of the wax ring. The challenging part here is that the ID of that red part is 5" so most wax rings don't seal properly. The challenge is that the ID is only 4" so most wax rings won't get a good seal. I found some posts on the Terry Love forums describing similar situations and the consensus was to use some sort of a "dutchman" for a solution.
    – Timv
    Feb 23, 2023 at 4:26
  • Anyway, I broke down and called my plumber who says he sees this all the time and is coming by tomorrow to fix it. I'll report back with what he does Thanks for your help. I appreciate you taking the time.
    – Timv
    Feb 23, 2023 at 4:26

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