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Thread: New floor drain in concrete

  1. #1
    DIY Junior Member albertalbert's Avatar
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    Default New floor drain in concrete

    I have flooded my basement for the last time. It's time to put in a drain. I'm an experienced DIY'er and am looking forward to this project. I was planning on having a few conversations at the plumbing supply store, but I wanted to get a few ideas here. Here's what I'm planning, so I'd love any feedback on what to do/not to do:

    I know where my laundry sink drain line is. I'm going to tie into that. Rent a jackhammer and get access to that (I'll be replacing the connection where the laundry sink drains into the floor as that is rusted over), then just make a line about 6" wide and go until hit where I want my drain. I am not sure what to expect as to how long this process will take.

    I'm assuming I just use a sloped 90 fitting, but I'm not sure. I heard that you need trap which makes sense, but I wanted to make sure. Does that trap work just like a normal sink/toilet trap, and is it right after the drain, or closer to the connection? I also heard you're supposed to run a water line out there to prevent evaporation from making the trap ineffective, but that seems like overkill to me (mild temps where I live most of the year).

    As you see, I'm not quite ready to start this yet. Do you have any pointers? Thanks!

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    Retired Defense Industry Engineer jadnashua's Avatar
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    First off, why did you get the flooding? A floor drain could make it worse under some conditions. The trap needs to go underneath the drain. Since it is connected to the sewer, and the drain may not get much use, a trap primer can help.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Moderator & Master Plumber hj's Avatar
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    "Mild temps" have NOTHING to do with maintaining the seal in the trap. And installing a floor drain is a bit more complicated than just putting a "connection" in the line and running a pipe in a 6" trench to wherever you want to put the drain.

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    DIY Junior Member albertalbert's Avatar
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    The connection from my laundry sink into the floor drain is rusted out. My fix for this has been shoving the PVC into the steel pipe below and caking the connection with silicone. If the dryer bounces a bit, it can break that seal. That line also needs to be snaked as the sink drains slowly (it used to overflow before I put some chemicals down there). So, it has flooded over the sink and also the plumbing connection has broken. Lastly we had an accident where the hose from the washer was "temporarily" removed from the sink (hurts to think about that one). All in all, a drain seems like a good backup plan, and I need to get under that concrete anyway to fix the sink connection.

  5. #5
    DIY Junior Member albertalbert's Avatar
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    HJ - If my history of projects has taught me anything, it's that there is always more to it than I originally plan on. As far as the seal in the trap, would you say a bit more on that? I assumed that the only thing that would break that seal would be evaporation. I also assumed that would happen more often/quicker in hotter climates. My dad's house has a floor drain, but no water lines connected to it, and he's never had an issue with sewer gasses, so that is why I am not sold on the need to run those lines to the trap.

    As far as the parts that are more complicated, any pointers are welcome. I'm planning on placing the drain at the low point in the floor, then obviously sloping the line 'downstream' to the new connection. I'd use the proper pipe size and connectors. Do you rest the new pipe on a pad of gravel or something before you pour the concrete over it?

    While you are in the slab, I would consider replacing pipe. Sooner or later, and it seems you are at sooner, it will be time.
    The line should be 2". Sometimes old cast pipe in the ground will perforate on the lower side, especially when chemicals are put in the line. Then the dirt from below starts filling the line. A natural drain cleaner is better with soap. Bio-Clean, which I sell here in Seattle.
    Last edited by Terry; 05-19-2010 at 08:54 AM.

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    Forum Admin, Expert Plumber Terry's Avatar
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    Any floor drain in Seattle needs a trap primer.
    They primer can com off the water supply or off a waste line, but either way, you would use a fitting on the vertical above the trap, and below the drain itself and that is where the water would drip in to keep a constantly filled p-trap.
    A tee on the standpipe of the washer that diverts water to the p-trap. Everytime you run a load, a bit of water would wind up at the p-trap from the water being discharged.

    Plumbing code doesn't really care how Dad's was done in 1920.
    Code has changed a lot sense then. I remember cutting out plumbing for a basement bath down near Michigan street, and Wow! the smell was bad.
    You will also need a vent between the trap and the wye where it connects to the main plumbing. Without the vent, the trap can also siphon.
    Last edited by Terry; 05-19-2010 at 08:59 AM.

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    Moderator & Master Plumber hj's Avatar
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    There are at least six ways for a trap to lose its seal, and evaporation is one of them. The area under the concrete floor is relatively stable as far as temperature is concerned so your "climate" is irrelevent.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    You may want the line under the slab to be larger than the 2" required for the standpipe and the trap. You need to check your local codes. If you repair the standpipe and line from it to the main sewer line, I'm not sure adding a floor drain really buys you all that much for the added costs for venting and priming. Now, if you wanted to hose the basement down, a floor drain might be useful, but then probably only if the whole floor was sloped to that drain, which is probably isn't.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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