Plumbing shower waste into basin waste

Discussion in 'Plumbers' Talk' started by Merdeindeed, Apr 17, 2018.

  1. Merdeindeed

    Merdeindeed New Member

    Hi - I'm about to plumb in my new ensuite. It will be a toilet, basin and shower. My current plan is for the the basin and shower wastes to go directly outside and then into the existing soil stack with a boss (on separate bosses). The toilet soil pipe will go directly out, through a 90deg bend horizontally and then into the existing soil stack. I was wondering if there is any downside to putting the shower and basin waste into the new toilet soil pipe which will have a 2 meter run horizontally along the outside wall before it goes into the existing soil stack. I am trying to avoid getting gurgling from the shower or basin - and was advised not to join them up inside the house before they reached the larger soil pipe.

    Thanks for the help!
  2. Dr Bodgit

    Dr Bodgit Well-Known Member

    AFAIK, the basin and shower waste pipes are different sizes ( 1 1/4" and 1 1/2") and you don't want to connected them together, they should each connect to the soil stack via a boss.

    Whether they could connect to the horizontal soil stack I don't know, its common practice to connect them to the soil stack when vertical.
  3. Merdeindeed

    Merdeindeed New Member

    Hi Dr B, thanks for the quick reply.

    The existing plumbing for the main bathroom sends the shower and basin waste on 40mm and 32mm pipes respectively to the soil stack where it taps in to the vertical . Starts to get tricky now because the main soil stack already has two bosses on it, so finding space for another two will require luck that they sit at the right height to allow the drop I need. Not impossible, just tricky. I did wonder as an alternative to bring both sink and waste out then drop the 32mm from the sink into a 40mm waste from the shower, then tap into the existing soil with 1 boss. Again, I am not sure if that will cause either the shower or the basin to gurgle or drain down. Seems the safest way would be to keep everything on dedicated wastes until the main vertical stack.

    Any other ideas welcome!!
  4. rogerk101

    rogerk101 Well-Known Member

    I would connect them both to a 40mm pipe run with only one connection boss into the 110mm stack.
    If you do happen to get any gurgling (which I highly doubt), you could always put in a 40mm AAV wherever you can fit it neatly, but that's only a last resort.
    I have done several runs like that - never use 32mm pipe if I can avoid it - and never had a problem.
    retiredsparks likes this.
  5. KIAB

    KIAB Well-Known Member


    Could even use a AAV trap for basin, but I doubt you will get any problem to need one.
  6. dcox

    dcox Active Member

    You're risking pulling the water trap out of the shower if you empty a basin full of water down a combined pipe, but as Roger says, adding a basin trap with an air admittance valve should help. I've had problems with leaky AAVs so try to avoid them if I can. Could you drop the basin waste pipe into a boss on the 2m horizontal section of new wc soil pipe and reuse an existing boss on the vertical stack for the shower?
  7. Merdeindeed

    Merdeindeed New Member

    Hi, thanks for all the ideas! Using 40mm for both wastes is a great idea. I don't have any space constraints and its all concealed in the house. Putting one into the new horizontal and 1 in to the existing vertical soil stacks might well be the best solution, i'll take a look at the layout and see how that might work.

    On the AAV's - I had heard lots of stories of them not being very reliable, and the pipework is for the most part going to be concealed and tiled over - so I need to avoid that!

    Thanks one and all.
  8. Pollowick

    Pollowick Well-Known Member

  9. Merdeindeed

    Merdeindeed New Member

    That would have worked too, but Im fitting a wall hung pan on a frame and the connector goes straight out the wall horizontally.
  10. Pollowick

    Pollowick Well-Known Member

    Is the frame 150mm off the wall to allow for the cistern? If so, there is possibly room there.
  11. Merdeindeed

    Merdeindeed New Member

    I had another idea. Is there any issues (apart from visual) in creating a 40mm pipe vent outside the wall? i would have thought that would address any vacuum issues. But would i need to run the vent to above the roof line, like the existing soil stack. Or i suppose run it into the vent stack at a higher I dont need a downhill run

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