How to design drainage for basement bathroom

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by sonicsmooth, Feb 1, 2011.

  1. sonicsmooth

    sonicsmooth New Member

    Messages:
    3
    Location:
    Seattle, WA
    Hi,

    We are remodeling the basement in our 1908 Seattle house, and wish to remove the existing sewer pump, NOT install any more pumps(!) (eg saniflow, etc.), and NOT build the bathroom or toilet up on a platform. We have to reconnect the sewer at a lower point, but due to a bunch of restrictions, we don't get a full 6" below the new slab we intend to pour, at the location where the bathroom is.

    So, How do we connect a toilet here? I've calculated that the top of the drain pipe just reaches the top of the new slab, if I take into account the 1/4" per foot slope requirements.

    I'm thinking the best solution for toilets is a floor-mounted rear-drain toilet (rear discharge, etc.) These typically have a 4" rough-in above the floor, rather than requiring 6" clearance below the floor.

    So I'm wondering:
    * Is this the appropriate use of a rear-discharge toilet?
    * Since I don't want to fur out the walls in the basement any more than I have to, am I allowed to go from the rear-discharge above-floor flange immediately to a 90-degree elbow to route the pipe under the slab? If not, what are the minimum radius requirements for pipe corners in drainage?
    * Do I legally need a 4" pipe since this will be a below-slab pipe, in the basement?

    * If rear-discharge is not the correct solution, is there a down-discharge (ie normal toilet) solution that allows the drainage pipe to be just *at* the level of the slab?

    * What is the most affordable rear discharge toilet?

    thanks
    Michael
  2. sonicsmooth

    sonicsmooth New Member

    Messages:
    3
    Location:
    Seattle, WA
    How deep must rough under slab be?

    I'm pouring a new slab over new sewer lines in the basement. I have almost zero depth between the top of the slab and where the drain pipes need to be, because of where we tie into the side sewer.

    So the question is: is there a *code* requirement for how deep under the top surface of the slab the drain pipes need to be? Can they be just under the top surface? 1"? 6"? etc.

    I may need to use 1/8" per foot instead of 1/4" like I've been assuming.

    thanks
    Michael
  3. Terry

    Terry Administrator Staff Member

    Messages:
    15,121
    Location:
    Bothell, Washington
    A bathroom set can use 3" pipe for the toilet.
    It's only when you add the fourth toilet that it needs to be 4"

    Horizontal bends are long sweeps,
    Going from vertical to horizontal is long sweep
    Going from horizontal to vertical can be a med bend.

    For the toilet, you may want to look into wall hung; they are about $300 more with the wall bracket then a floor mount rear outlet toilet.
    Toto makes a Wall hung dual flush Aquia with Sanagloss with in-wall tank and mounting bracket for about $980 list, $686 my price
    http://www.totousa.com/ProductDetai...SearchId=242fa191-20a3-48e7-aad9-e185212b8086

    It's nice to have at least 3" coverage over the pipe with concrete. Though you may be able to get by with a bit less.

    Toto CT418 wall hung bowl
    [​IMG]
    Last edited: Mar 9, 2011
  4. sonicsmooth

    sonicsmooth New Member

    Messages:
    3
    Location:
    Seattle, WA
    Great, thanks for the input. I think I don't completely understand how the in-wall tank is accessed. Does this model use pressure assist or gravity only? How well does this flush compared to the others?

    Thanks again, I enjoy this website very much.
    Michael
  5. Terry

    Terry Administrator Staff Member

    Messages:
    15,121
    Location:
    Bothell, Washington
  6. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,815
    Location:
    Cave Creek, Arizona
    quote; I have almost zero depth between the top of the slab and where the drain pipes need to be, because of where we tie into the side sewer.

    Here, because a pipe IN the concrete creates a weak spot that WILL crack, we cannot do it unless we resort to extensive reinforcement above the pipe. Your questions imply that you are in "over your head" to try this as a "first time" DIY project. There is absolutely NO WAY to install a floor outlet toilet on a drain line that is less than 2" below the top of the slab, and even that would be pushing the envelope.
    Last edited: Mar 10, 2011
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