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Does basin waste pipe need 'drop' under floorboards?

Discussion in 'Plumbing and Central Heating' started by robodelfy, 5 May 2020.

  1. robodelfy

    robodelfy

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    I'm just about to run my previously exposed sink feeds and waste pipe into the wall cavity.

    I notice the horizontal part of the waste pipe that runs a couple of meters and joins the bath waste and goes outside, it just lies on the floor. Does it need to have a drop so the water drains outside? I can only imagine water sitting in it constantly otherwise, maybe that doesn't matter?

    20200505_151616.jpg
     
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  3. terryplumb

    terryplumb

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    Yes,it should have a fall ,downward slope ,as should all waste pipework.
     
  4. robodelfy

    robodelfy

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    And how would this normally be done, just a little support at one end? Also, surely they would have thought of this before, but I don't see any drop, its just running along the floor
     
  5. terryplumb

    terryplumb

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    Horizontal waste pipes would be clipped ( pipe supports ) every half metre ( roughly) to prevent sagging . Some don't give a **** and do as they please. Bit like people who drive at 50 mph in a 30mph zone, cos they are in a hurry and they know full well they shouldn't.
     
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  6. robodelfy

    robodelfy

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    Thanks, good to know. So in my situation, you can see the waste runs between the two copper pipes. I guess I can just cut varying size bits of wood to create a drop from start to finish. Is the an idea angle to try and achieve? I can't raise the pipe much as the ply will be going on top of it
     
  7. terryplumb

    terryplumb

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    From memory ,I think it's minimum fall of 18mm per metre . But happy to be corrected , my memory isn't what it used to be :D:D:D
     
  8. robodelfy

    robodelfy

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    Wow thats a lot more I thought, it would add up to quite a height after a few metres! I guess I'll just do the maximum I can, and chock it up with some little wood blocks
     
  9. Jackrae

    Jackrae

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    The reason for a run is basically to ensure a dry line for a couple of reasons (or maybe three )
    a) To prevent stagnant water getting frozen and building up an ice dam. As the pipe is internal you can ignore that one
    b) To prevent the collection of waxes etc from soap, hair and skin building up and blocking the pipe. Can't be avoided but use of an occasional drain cleaner will eliminate the problem if it ever arises.
    A flat sink drain may not be 'right' by the book but if it meets your needs then you have to do what you have to do.
     
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  11. And dismantle your wall when the pipe blocks
     
  12. robodelfy

    robodelfy

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    The issue I realised today is that I can raise the pip at all because there is no space under the floor boards. I don't really know what the solution would be to get some fall
     
  13. terryplumb

    terryplumb

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    Run it on the surface ,and box it in ? Run it thru two studs and bring it down in the corner ?
     
  14. robodelfy

    robodelfy

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    Hmm, what about joining it to the larger toilet waste, is that possible? Currently it runs to the opposite side of the room and I can't get to most of it without ripping everything up
     
  15. terryplumb

    terryplumb

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    Sounds like an awful long run of pipe, and a load of hassle for no real gain.
     
  16. OwainDIYer

    OwainDIYer

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    one inch per metre is about right, if you don't mind me mixing measurements.

    that's 1 in 40 gradient.
     
  17. Nige F

    Nige F

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    What does it do outside ?
     
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