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Thread: DIY sewer line replacement (partial) ?

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    DIY Junior Member JLM34's Avatar
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    Default DIY sewer line replacement (partial) ?

    Hi.. I am needing to at least partially replace some sewer line. The issue at hand is that at one end of my house (kitchen and laundry) I have some issues with either corroded or broken (or both) 40 year old iron drain pipes under the slab. The main sewer line that runs to the road is on the opposite side of the house, so these lines run all the way across the house under the slab and tie in with everything else. In talking with a plumber, he said an option for me to avoid the whole jackhammering the slab up is to simply run a new line out of the side of the house, down the brick, and into a new PVC 3" line and run that clear around the house, then tie into the existing line close to the house. Is this generally something that is legal for a DIYer to do at his own home legally? The plumber stated that there's no specific code on how deep this line would have to be other than it cannot be exposed. I guess our climate here is such that depth is not all that critical. Basically my plan is to dig this approx 120 foot trench (after locating underground utilities, of course) and laying schedule 40 3" PVC, pitching it 1" per 8-10 feet. I won't be tying into the city's main or anything like that. I simply cannot afford to pay someone $85-100 an hour to dig a trench for me. I'm capable of laying the pipe with the correct pitch and making all the connections properly. I do realize there will be some capping off issues of the old line and re-tying things back into the vent and such, which I'm fine with hiring out. Anything I should look out for or advice on laying the new sewer line for this "gray" water? Thanks.

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    In the Trades Tom Sawyer's Avatar
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    On the face of it is sounds like a viable solution but check with the plumbing inspector first because Up here we can't run 3" it would have to be 4". Texas might be different though.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    In the Trades Gary Swart's Avatar
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    I believe the slope has to be at least 1" per 4 feet, so you will need at least a 30" change in depth from where you begin to the main sewer. You don't need to worry about sewer lines freezing except in places like Fairbanks, Alaska. There should never be standing water in a sewer, so in most places water will reach the sewer before it can freeze. Don't know about size minimum in your area, but the cost difference between 3" and 4" should not break the bank.

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    DIY Junior Member JLM34's Avatar
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    Thanks for the replies. 3" is all that's required here. It looks like you guys live far far north from me. I take it maybe the codes can be quite a bit different in different parts of the country. Two plumbers I've talked to said 1" per 8 to 10 feet. Maybe that's more of a regional thing due to our lack of much freezing weather? One of them, while specifically stating I do need to make sure it is pitched for flow, said hypothetically I could have sections of level pipe and even some slightly uphill and that a 3" line would still flow. Obviously, he wasn't trying to downplay the importance of the pitch or anything, but he was just shooting the breeze I guess. I was planning on testing each section of pipe for flow before I continued on to the next one. As in run a little water down the starting point to ensure it flows out the other end. I figure if the water comes out the other end fairly quickly, then surely it has enough pitch.

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    In the Trades Gary Swart's Avatar
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    While I'm not a professional plumber, I have been frequenting this forum for several years. I have read anything that deviates from the 1" fall per 4' length. Nor have I read of anyone who could make water under gravity flow uphill. In fact, one of the problems of drain clogs is a low spot in the line. I would bet a sizable sum that professional plumbers would have a bit more scientific way of determining proper slope that what you suggest doing. You might undertake digging the trench, although without a backhoe that could be a problem, then hire a plumbing contractor to install the line. Of course the best way would be to contract the entire job. I believe you're stretching DIY.

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    DIY Junior Member JLM34's Avatar
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    An inch per 4 feet?? I'm in no position to argue plumbing really, I'm just saying I was told 1" per 8-10 feet by two plumbers here. Perhaps plumbers have a more precise way of measuring the proper fall, but a real world test doesn't lie, does it?? But...yes, I will also have a level on hand to ensure there is fall. Maybe I'm stretching DIY, but I have a lot more muscle and energy than I do money at this point so I have no choice. I don't know if he literally meant water would flow uphill. I guess he was saying if a section was level rather than had fall, the system would still hypothetically work, only that section of pipe would hold a little water..

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    Test, Don't Guess! cacher_chick's Avatar
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    While most drain piping is pitched at a minimum of 1/4" per foot, our code allows a minimum 1/8" per foot for lines 4" and larger.

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    Plumber jimbo's Avatar
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    One inch per 10 feet is below any code. The most common number is 1/4" per foot, which is 2˝" in 10 feet, and often you will be allowed to use 1/8" per foot for 4" pipe and larger. That is 1 1/4" in 10 feet.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    You need the slope AND you absolutely do NOT want any level or uphill sections! Those slopes are the MINIMUM, more is okay. You're limited by the depth of where you make the connection into the existing line. Locate that and verify that you have at least the minimum slope. If you do, you should be okay. If not, you may need to rethink this.
    Jim DeBruycker
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    In the Trades Gary Swart's Avatar
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    If anyone has a problem with the math, 1/4" per foot is the same as 1" per 4 feet.

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    Plumber Winslow's Avatar
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    Water flowing through a pipe via gravity has it's maximum pipe scouring capabilities at 2 ft per second, which is 1/4 inch per foot. That is why codes usually require drain lines 3" and under be pitched at 1/4 inch per foot. Water will still flow through a pipe with less pitch and even level, but will eventually build up matter on the pipe walls and clog because drain lines carry particles in suspension and solids.

    Regarding paying a plumbers wage to dig trenches you could always dig the trenches yourself and then pay the plumbing contractor to lay the pipe.

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by JLM34 View Post
    ... to simply run a new line out of the side of the house, down the brick, and into a new PVC 3" line and run that clear around the house, then tie into the existing line close to the house. Is this generally something that is legal for a DIYer to do at his own home legally?
    As long as you are the homeowner, I think the only place there would be trouble would be if you were going past the curb and doing anything under the street.

    My house is similar to yours with the kitchen and laundry at the far end, and whatever fall you have between there and your sewer line will be fine. Just use a string while bedding it to be sure it has no sags.
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by Winslow View Post
    Regarding paying a plumbers wage to dig trenches you could always dig the trenches yourself and then pay the plumbing contractor to lay the pipe.
    I tried that last year while installing a new sewer line. I rented a trencher and dug down to the pipe, but then the plumber wanted to bring in his mini-excavator and really tear things up so he would not have to lay on his belly and reach down into the trench. I do understand he had paid his dues with a shovel many years ago, but I just finished the job myself.
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

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    DIY Junior Member JLM34's Avatar
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    Thanks for all the input. I'll have a 4 foot level so I will experiment with what exactly a 2" drop every 10 foot looks like on the level. I had thought about what depth I would be at once I got around to the main line. I need to locate it first and see how deep it is. So....could you ever have TOO much fall in the pipe? I ask this because my Plan B would involve going another route and tying in a new place to the city sewer. Obviously, I couldn't do some of this myself legally. If I went that direction there's probably a 10 foot drop in 70 feet from the house to the street. Obviously, if I stuck with 2.5" drop every 10 feet to the city's line, that would require one heck of a deep trench in places. How are situations like that handled?

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    Plumber jimbo's Avatar
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    Sewer lines are underground. You have to deal with that. Place a 0.8" thick block at the end of the level. If the slope is at your 2" per 10', the bubble will be right on.

    There is no such things as too much slope. The best drain lines are vertical!

    I would say the first thing you need to find out is what depth the sewer is at the point you want to tie into it. Since you have a long run around the house to get there, and it must slope continuously, that just may not pencil out.

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