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Thread: New Construction Drain Question

  1. #1
    DIY Junior Member rainier's Avatar
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    Default New Construction Drain Question

    Hi Folks,

    I've picked up a lot of good ideas here, but I haven't come across anything addressing this.

    I'm building an 800 sq ft cabin in Idaho and will be doing the plumbing this spring. I have a crawl space under the cabin with 3' walls on an 8" footing. The bathroom will be in the SE corner and that is also where I tie into the septic tank. The toilet will be 5 1/2' from the S wall along the E wall. The 4" line to the septic tank is about 2' below the bottom of the floor joists which means that there is about a 3' drop from the bathroom floor to the septic drain pipe. The kitchen is next to the bathroom along the E wall. So, all of the plumbing is short runs along that side of the house with essentially a straight shot to the septic tank. I plan to use 3" ABS from the toilet to the septic line.

    My question is: do I drop straight down from the toilet and tie straight into the septic tank or should I drop down and clear the floor joists, run horizontal to the S wall and then drop down and tie in to the septic tank? I have plenty of room in the crawl space to tie in the drains from the washer, lavatory, kitchen sink and the main vent stack.

    I appreciate any help or suggestions.

    Rainier

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    Normally the septic tank is outside the foundation of a home.
    The plumbing in the cabin or home, drops through the floor, and ties into horizontal lines in the crawl space, and eigther through the foundation, or under depending upon the frost level on the ground.
    It won't do you much good if it freezes.
    You will need to run vents or vent up through the roof.

  3. #3
    Test, Don't Guess! cacher_chick's Avatar
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    Local codes should specify the depth required to pipe below the frost line when existing the structure. Every fixture trap must be properly vented, or your cabin will end up smelling like your septic tank.

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    Moderator & Master Plumber hj's Avatar
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    quote; Local codes should specify the depth required to pipe below the frost line

    That has nothing to do with sewer/drain lines. You install them as required to connect to the "sewer system" REGARDLESS of how deep they are. Sewer lines do NOT freeze unless they have a continual, very slow, flow of water through them, which only occurs when something is leaking. As for the original question, it makes no difference, although the most direct flow is usually the best.
    Licensed residential and commercial plumber

  5. #5
    DIY Senior Member Reach4's Avatar
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    Running the toilet and the rest of the bathroom straight to the septic tank tank after dropping below the frost line, will probably give you more space in the crawl space, and would mean that a blockage in one line to the septic tank would permit the other line to continue working. It's not as much redundancy as if two bathrooms were on different pipes, however. Yes, the bathroom needs a roof vent, but you would have that anyway.

    If the excavations were complete, you would just tie into the existing connection. With the backhoe work not completed, this option is open. I have more than one connection to my septic tank.

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    DIY Junior Member rainier's Avatar
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    Thanks Guys,

    I don't have a problem with what you've addressed. I was just wondering if it's normal to plumb a straight shot down from the toilet about 3 feet and then make a turn direct to the septic tank, which is outside, or should it turn horizontal just under the floor joists, 12 inches below the floor, and then turn down again at the septic tank connection.

    Thanks for the help,

    Rainier

  7. #7
    DIY Junior Member rainier's Avatar
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    Thanks again Folks,

    I was typing while you were replying. I'll take the direct route and drop down to the level of my septic line direct from the toilet.

    Rainier

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