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Help with Plumbing a double wall hung Sink and vanity unit.

Discussion in 'Plumbing and Central Heating' started by Superflo, 12 Nov 2020.

  1. Superflo

    Superflo

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    I have some experience with plumbing a single wall hung sink and vanity unit, I brought the waste and hot/cold pipes up behind plasterboard and through the wall, pretty straightforward. I am now looking at fitting double wall hung sink unit, therefore my plan is to bring the hot and cold up behind the plasterboard and through the wall, then add a t piece to allow both hots and colds to be fed. Were I'm struggling is how I run the waste for both, I thought i would have done the same as single, then used a mcalppine double sink kit, but when I look at these, they are only suitable for 40mm, not 32mm as required.

    Could you please verify the above suggestion around feeding the hot and cold and I would appreciate any suggestions on how I approach the waste for both sinks, does each sink need a trap? etc..

    Many Thanks
    Cameron.
     
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  3. oldbuffer

    oldbuffer

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    1. Basins generally use 32 mm (1 1/4") waste pipe and traps. As you say, McAlpine only make the double ones for sinks, which are 40 mm (1 1/2").
    2. The basins each need a trap, although you might consider using a running trap on 50 mm pipe as non-preferred alternative.
    3. So, trap to each basin. Come off the traps in 32 mm, then either:
    3a. Off basin furthest from stack in 32 mm down and across toward basin nearer stack.
    3b. Off basin nearer stack, down in 32 mm, then towards stack in 40 mm, with 32 mm pipe from other basin coming in to end of 40 mm pipe.
    4. If the run to the stack is long, consider uprating to 50 mm pipe at an appropriate point.
    5. With respect to the hot and cold, sounds fine. You should add isolation valves. Given how close the basins are you could fit them before the tees to cover both basins, bit it might be easier to fit one to each hot and cold to each basin. Use decent quality full bore valves.
     
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  4. Superflo

    Superflo

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    That's great, just for clarity, see attached image. Does this look about right, the grey pipe is all 32mm, were the arrow is. there should be a line showing the floorboard level, also I read somewhere that fitting 2
    traps can cause air pockets blocking one or the other's drain, not challenging just trying to understand if this is acutely correct. Thanks Cameron.

    upload_2020-11-12_17-52-12.png
     
  5. Madrab

    Madrab

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    If both basin could be used/drain at the same time then you want to increase the pipe to 40mm were they tee together and make one of them an anti vac trap.
     
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  6. Superflo

    Superflo

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    thanks Rob, both could be used at same time, just to clarify, do u mean run 40mm pipe from tee down to the stack? C
     
  7. Madrab

    Madrab

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    Yup, you would actually use a 40mm elbow and a 40mm tee to ensure there is no crossflow.

    On a 40mm vertical pipe down into the stack then use a 40mm swept elbow onto the top with a 32mm reducer for one basin and then a 40mm tee would go in a little further down with a 32mm reducer for the other basin. Put the anti vac trap on the basin draining into the lower tee.
     
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