I am about to tile a bathroom floor. I was dry-fitting some concrete board when I realized I don't know how the toilet will reconnect once the floor is higher.

Concrete boards dry fit on floor with toilet pipe

The old floor was a thin layer of vinyl adhered directly to the subfloor. The new floor will be roughly 1/8" thinset mortar + 1/4" concrete board + 1/8" thinset mortar + 1/4" tile. So almost 3/4" higher than the old floor.

The PVC toilet pipe is 4" interior, 5.25" exterior.

Toilet pipe from above

The bad news: it's an offset, something like this.

Offset toilet pipe

It had a broken metal flange permanently attached to it. I have already broken away the flange.

It looks like people who are tiling usually do one of two things. Sometimes they leave the old flange on the sub-floor, and use some extension system like Set-Rite to raise the height to a second flange.

Alternatively, they just install a flange on top of the tile, and some sort of gasketed pipe descends into the old, lower 4" PVC pipe.

But what about the offset? Because of it's angled, funnel-like shape, I can't just run another pipe into it, can I?

I feel like I should cut the PVC below the subfloor, and reinstall a new offset valve higher than the old one. But space is cramped beneath the floor, and I'm afraid I'll make things worse.

Toilet piping below floor

Toilet piping below floor close-up

I saw some videos online about separating PVC with extreme heat, but I'm afraid of igniting my house or sewer gases (I have a septic tank) or both. I have minimal PVC experience.

2 Answers 2


What you are looking for is a riser also called extension flange. But considering you are able to get to the pipe below - you could just extend it to what you need, but cramped space and a crappy job - and possibly not being able to seal it properly well - could be really ...

Humor aside take a look at the links here I think you will find it to be easier.

I do believe they make spacer flanges in @ 1/2 and 3/4 inch increment.

See this link Extension Flange

There is more detailed information provided here for 4 options but extenders and spacers are straight forward and simple.

Extension Flange

  • If I layer an extension flange on top of another flange, won't I have two flanges, with no sealant between them? The actual waste pipe will be lower than the height of my extension flange. I can see that the wax ring will seal the toilet to the extension flange, but what will seal my extension flange to the waste pipe?
    – Michael H
    Commented May 6, 2017 at 19:54
  • 1
    @MichaelH there might be a gasket with it - but normally they are caulked a sealant is placed on top of the old flange and you attach the new flange directly on top of the old. Extenders have a lip that drops inside the existing pipe, Spacers require caulk. I will post a link in my answer.
    – Ken
    Commented May 6, 2017 at 19:59

Plumbing trick...You are basically going to make a coupling out of 4" PVC pipe. Cut 3" pipe below the floor even with the top of the hub on the 3" elbow. 4" PVC pipe will fit perfectly over the 3" hub at the top of the elbow. Glue 3" hub to the inside of the 4" pipe. Next, your "new" offset flange hub will glue into the 4" pipe.

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