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This question is related to Can you run two toilets on the same horizontal soil/waste pipe?, but is a different question.

Our house used to have only one toilet, with a waste pipe running downhill by a couple of degrees until it exited the wall of the house, where it branched into a vertical pipe.

Then at some point, someone added another toilet, and to make the pipe work easier, changed the pipe to be horizontal.

Horizontal waste pipe

Then we bought the house. We noticed that the toilets don't flush that well, the water takes a bit of time to drain out of the bowl. We asked a plumber, and he thinks it's because the waste pipe is horizontal, and not angled, as it should be.

I can understand why they made it horizontal. I can see that it would be very difficult joining toilet 2 to a waste pipe that was a couple of inches lower.

Angled waste pipe problem

What are my options here?

Option 1: Use an offset fitting, plus a branch. This would work, but the offset would push the toilet away from the wall a couple of inches, which I would prefer not to do, since it's a very small bathroom.

Option 2: Is there such a thing as an offset branch piece, to allow Toilet 2 to connect to the lower pipe?

Is there another option?

Note: There is very little space available around Toilet 2. There is no room to run two separate pipes.

Rocketmagnet
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4 Answers4

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The wye for the second toilet is turned up towards the second toilet, and another angled fitting (one of the smaller angles, typically) is placed into it, with the rotation of the second and the wye adjusted to meet the toilet outlet.

If it's built as illustrated that may require moving the line, as there's no space as shown. But you'll be moving the line somewhat anyway to correct the slope.

I don't know what the UK allows, but under IPC plumbing code that configuration would require a vent near toilet 1. The permissible unvented connection to a stack with vent is fairly short, and for only 1 toilet on the line. This looks too long even for the one.

Ecnerwal
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Replace the bowl of toilet 2 with a right-hand p-trap type and run two separate horizontal drains.

A right hand p trap has the pipe connection to the side of the toilet bowl instead of to the back thus it can have a separate lateral pipe and separate connection to the stack.

Jasen
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If the distance between the toilets is not very far you might be able to raise Toilet 1 onto a small plinth so that the waste pipe hits Toilet 2 at the correct height. The further apart they are, however, the greater the height required so unless they are close together this suggestion won't work.

PaulH
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You can support up to 3 toilets on a 3" line and 4 toilets on a 4" (there are other rules). But you can for sure have two toilets on a 3" line and just make sure the slope is 1/4" down per foot. You need 3" combos for each connection to the "horizontal" drain.

DMoore
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