Add second toilet to soil pipe

29 Aug 2010
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United Kingdom

We are redesigning our bathroom and want to partition it to create a second toilet.

The existing toilet is by the bathroom entrance so this would stay in place and become the closet toilet. We then want to add a new toilet in the bathroom.

The new toilet will be on the same (external) wall, about 1 - 1.5m further along.

The waste from the existing toilet goes straight through the wall and into the vertical soil pipe. I think I need to break into the soil pipe below the existing connection and add a branch connection to run horizontally to the new toilet.

If I put the new branch directly below the existing toilet connection then I estimate it will enter the soil pipe about 380 - 400mm below the toilet outlet. Given that I have around 1m horizontal distance to the new toilet that gives a drop of around 1:3. This is much more than the 1:40 I see quoted as ideal. Is it too much?

The only alternative I can see is to have a short vertical before turning and running horizontally to the soil pipe. Is this an acceptable layout?

Any other ideas?

Thanks for your help.

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The fall wont be too critical over that distance (unless you ask it run uphill from the toilet!). The 1:40 is for long distances, especially with underground drains.

If your stack is plastic you have the option to fit a double branch in place of the existing single branch, provided that will give the required fall.
Thanks Hugh.

I think I'd struggle to get the fall using a double branch

Sounds like dropping the new pipe in below the existing branch will be no problem though so I'm happy with that.

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1 in 40 is a minimum fall; you can have more. You'll need to create a slip joint below the existing branch.

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