DWV Cottage Rough In Questions

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by chuck b, Jun 12, 2012.

  1. chuck b

    chuck b sea-bee

    Messages:
    78
    Location:
    levering, michigan
    RE: 800 square foot Northern Michigan Cottage

    Hi Guys,

    Preparing to rough in the DWV System in advance of the new Septic Field installation. The inadequate old DWV system has been removed and trashed. The septic installer can connect to either a 3" or 4" Sch. 40PVC DWV system. Wondering if in a small 2 bedroom cabin, considering a 1.6gallon flush toilet, the 4" would be better? Cost is not a big issue as this is a small cottage. Is there a measurable benefit? Please comment.

    Also, when plumbing the toilet, is a "Wide-Sweep 90 Degree" fitting better than a "Closet Bend" directly below the toilet closet flange and vertical pipe?

    When connecting the HORIZONTAL toilet line to the 3 or 4" main drain line (and this is all underneath the cottage which is built with a post and pier/joist set-up so the area is accessible), which fitting set up would make the toilet waste flow better: a "Y" fitting with 45 degree elbow combination, or a regular "Y" fitting, with a 45 degree fitting below the low heel vent 90 away from the "Y" fitting?

    What is the best way to stabilize drain and vent pipes in the wall and reduce noises...metal or plastic plumber's tape, and would it be a good idea to wrap the vertical pvc pipes in a gasket material before strapping? Is using wooden wedges a good or bad idea? I realize that expansion and contraction are issues. Should one use the aerosal "Great Stuff" foam fireblock, or is that just for where the vent pipes penetrate up through the top plate.

    the cabin is not heated in the cold Michigan winters if that matters. Supply pipes blown out of course. What would you do about winterizing the 40,000 gr water softener?

    Appreciate the feedback.

    Chuck
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,034
    Location:
    Cave Creek, Arizona
    800' or 8,000', it is immaterial. The basic rule is "the lower the flow, the SMALLER the pipe in order to maintain velocity", so a 3" pipe would be preferable. I have no idea, from your description, how you intend to connect the toilet to the piping. There are several right ways and a myriad of "wrong" ways, and a "low heel 1/4 bend" is usually in the "wrong" column.
  3. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,265
    Location:
    Maine
    Code won't allow anything smaller than 4" through the foundation. If it's doesn't have a foundation then you still need 4" from the septic tank to just inside the building perimeter.
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,034
    Location:
    Cave Creek, Arizona
    quote; Code won't allow anything smaller than 4" through the foundation

    What code is that? I have NOT used a 4" sanitary line in decades, unless the building had four or more toilets, which an 800 sq. ft. building in not likely to have.
  5. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,265
    Location:
    Maine
    The lateral from the foundation (building drain) to the septic tank or city sewer can't be less than 3" IPC and UPC
  6. Terry

    Terry Administrator Staff Member

    Messages:
    15,295
    Location:
    Bothell, Washington
    In Washington State the sewer has to be 4" or larger.
    The pipes inside, and stubbed 24" out can be 3" if no more then three toilets.

    A 3" pipe does carry better though.
  7. chuck b

    chuck b sea-bee

    Messages:
    78
    Location:
    levering, michigan
    Thanks terry

    Hi Terry,

    Great chance to say how interesting and instructive this forum has been. Thanks! Chuck

  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,034
    Location:
    Cave Creek, Arizona
    In most, if not all of Michigan, a 3" sewer to the main or septic is allowed for up to 3 toilets..
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