P-trap issue - Is it possible to switch washing machine and bathroom sink locations?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Linda49, Aug 30, 2010.

  1. Linda49

    Linda49 New Member

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    Aug 30, 2010
    Location:
    Texas
    I would like to incorporate the adjacent laundry room into the master bedroom and swap the washer dryer location with the double sink. Both drains are 2" emerging from the concrete slab. However, last night I discovered that the washing machine's P-trap is not really missing but simply hidden below the slab. Can I still put a pair of sink drains in above that P-trap?

    Thanks so much for this great forum, Terry. And thanks to all the regulars and moderators that are so helpful with their advice. I have learned a lot from reading the threads. I have mainly learned that I need to ask questions before proceeding.

    Linda
     
  2. jimbo

    jimbo Plumber

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    Location:
    San Diego, CA
    Code-wise, you have some issues. In NEITHER case, should the trap be below the floor. And the laundry drain should not be shared with other fixtures before it joins a main lateral. Presumably that lav. drain shares with tub and it may even be wet vented, which is also not allowed for the washing machine.

    If everything drains well now, it will probably work ok if you switch. But a permit might raise these issues.
     
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  4. Linda49

    Linda49 New Member

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    Hi Jimbo,

    Thanks for your quick answer. We have never had a drain problem. All the plumbing lines are grouped in the center of the house with a centrally located lateral main using shortest possible supply and drain runs. The master bath is the last group before the main goes to the septic system. The double sink where I want the washing machine to go is the last fixture on the grouping, and it has a vertical 1 1/2" vent extending directly above the 2" drain all the way through the roof. The washing machine doesn't have a separate vent where it is currently. It is centrally located between the the shower drain in the master bath and the shower drain in the main bath. I am not sure whether it shares the bathroom drain lines or joins the lateral main between the two baths. It could share the lateral between the bathtub and shower drain in the master bath since there is no seperate vent. Or could the plumber have figured that the opening around the discharge hose would serve as the vent?

    The house was built in 1985. No code enforcement other than septic system and electrical main inspections. A local plumber was talking to my husband and mentioned that the p-trap may be below the slab, so apparently that was not unusual back then. I bobbed for the p-trap last night, and the bob came up dripping wet.

    Question: Would relocating the sink p-traps above the old washer p-trap create a siphon issue, or is the old p-trap the only thing that would cause a siphon and that couldn't since there would be no fixture using that p-trap separate from the sinks?

    Another question: If we locate the washing machine stand pipe near the old sink drain with the vertical vent directly extending through the roof and with no other fixture vented above into that vertical vent, do we need to make a seperate vent between the washer p-trap using a long sweep 90 wye and tie in 6" above the the stand pipe height as is shown in Terry Love's wonderful photo of a standpipe/vent/p-trap, or is that separate vent loop unecessary in this case?

    Thanks again.

    Linda
     
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Two traps in series will cause problems. You'd want to replace the trap in the floor with one up at a normal position, and run a vent for it to prevent siphoning (and meet current codes).
     
  6. geniescience

    geniescience Homeowner

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    ditto
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    If the current washer standpipe is short, then maybe its total height is OK in relation to the P trap, and if so the thing about code these days is that P traps are supposed to be inside the same room as the fixture they serve. Except showers. To me that is not a big deal. But when renovating, we often seek to upgrade everything to meet the current code. Hmm. As Jimbo said, consult local authorities about this.

    The drain you describe for your washer standpipe is built as if designed to become a shower drain without any modification. That is one advantage I see to placing it under the slab. As for its venting, I'll guess it has to be self venting (less than X distance developed length with a 1/4" per foot slope) ; for more about this, search using these two key words: "trap arm".

    I'll guess this is a slab on grade, not a slab that you can walk underneath.

    As for this:
    I'll re-read it several more times. It'll communicate more if you draw a floor plan diagram, even if some parts of it are blanks. Running a new washer drain might be best.

    Only have one P trap, not two in a row (a series). Search using these four key words: "tubular continuous waste assembly" to see how sink drains get connected together before the drain goes to a common P trap.
     
  7. Linda49

    Linda49 New Member

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    Location:
    Texas
    Thanks Jim and geniescience. I drew up some pictures to help clarify. I've looked at altering my plan to use the the washing machine p-trap for a shower. It might work if there is a tool that can cut a hole around the pipe into the concrete slab deep enough for a drain to settle over it and be flush with the floor. I'd need a trench drain as the shower would then occupy the former utility space (see image) and the drain would be against the wall. The shower is to be curbless, but the current floor level is about 1 1/2" lower than the finished floor is expected to be so there would be enough slope to the drain.

    PlumbingMBath.jpg

    Below is a drawing from photos I took when the slab was being poured except I have adjusted the wall plates to reflect our updated design. The standpipe for the washer is in the middle. That's where I plan to put the sinks now. Breaking the slab to remove the p-trap isn't an option, however.

    PlumbingRough.jpg

    The water heater is electric.

    If I changed the plan, can the washer and bathroom sinks use the same drain back to back?

    Our reason for remodeling is to make the home suitable for wheelchair use. We plan to age in place, and this is the last remodel we will be capable of doing ourselves. The house was never built to code. It was built green before people knew what that meant.

    Linda
     
    Last edited: Aug 31, 2010
  8. geniescience

    geniescience Homeowner

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    ditto
    Location:
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    Definitely remove the P trap where the two sink drains join, if you are leaving the P trap under the floor.

    There is already a P trap in that drain line, and you must not install a second one in series. This was already mentioned at least twice yesterday. This is now the third time you have read this fact in this thread. Never have two P traps in the same drain line. This is now the fourth time you have read this fact. If I write it out again, in a different way, you will have read it five times. Your two sink drains get connected together before their now-common drain pipe goes to a common P trap, which is (I guess) the one under the floor, if you end up keeping that P trap and using that pipe for the two sinks. Hope it makes sense.

    To compensate for the large distance that water would fall to the underslab P trap, you can make that drain pipe go like a Z down to the floor. Web search using "offset drain" to see examples. The angles can be sharper than the offsets you will see in web searches showing products called offset drain. You can build your own offset with fittings, and with sharper angles. Having said this, I'm assuming you will have consulted some local authorities for their blessing. The idea is to break the fall, so that water rushing down the pipe doesn't scoot through the P trap entirely. This is because a P trap must have some water remaining in it, which is what they call "trapped" and that make the P trap function as it should. Otherwise it's not working as intended, and it will let sewer gases into your house, and this is a major health risk, a matter of life and death. I'm not a plumber so this entire paragraph may get knocked out later by Master plumbers who may tell you that it's just not going to meet their blessing to plan to install an offset to break the fall. In which case a localized concrete slab break and repair job will be required, to remove that existing P trap. Not a big deal. Easy as pie. You can even learn how to do this by reading on the internet.

    2/
    Here is one source for trench drains: myshowergrateshop.com
    They are less than one inch in height. http://www.myshowergrateshop.com
    The wetroom concept or bathroom floor as shower pan concept is a great idea.
    A channel drain (a long line) is great for making a flat (sloped not level) floor inside the shower pan.
    Very elegant.
    You will still need a slope, so there will still be a threshold to step up over; in other words it won't be a curbless shower -- unless you can figure out how to raise the floor in the corridor outside the shower, or you just cut a groove in the slab for the trench drain.

    The shower drain's "male exit" slides inside your existing 2" pipe.
    It doesn't matter that this reduces the diameter of the pipe at that one point.
    It's not significant, and it's not a code problem.
    You might need a bushing since the shower might have a 1.5" exit.

    3/
    About the extra venting I have no clear answer for you.

    4/
    The alternative plan you asked about is a no-no, as far as I know. (draining the washer suds into the same pipe as the sinks drain into.)

    Whether or not the entire plan is sound from a DWV point of view, is not something I can comment on.

    Everything i have written above is partial information.
    There is more to know.
    In addition to all that i have not yet written, there is a lot of other information that i don't know and which will be important to your specific case.
    There are inevitable corrections to what i have written above.
    Take no action based on having learned anything in this post.
    Get other information from other sources.
    Consult local authorities too.


    Hope this helps.
     
    Last edited: Aug 31, 2010
  9. Linda49

    Linda49 New Member

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    Location:
    Texas
    Hi geniescience,

    Thanks. I really appreciate your thought provoking reply and the link. I do understand about the extra p-trap where I was proposing to locate the double sink. I thought that would be a no go. That's the main reason I posted. I like your idea of using it as a shower drain instead. Great news about the drain fitting being a male. I'm really liking the trench drain placement there because it gives the toilet more room than the location of the current shower. The whole floor of the master bath will be raised about 1 1/2" so the shower won't require a curb.

    I am stuck on where to put the sink while still maintaining the wheelchair turning radius I want. I don't know if the p-trap where the washer currently is can be dug out without great difficulty. According to the plans, it is right where a slab beam is. The other p-traps are easily accessible through the boxes that were placed for them before the slab was poured. I can probably use the tub drain for a sink by removing the p-trap there. I can put in a vent there too. Really screws up my plan, though.

    I'm not sure you are correct about not using the same drain for the sink as the washing machine. The reason I say that is because it would be the exact same layout as Terry Love's picture of plumbing a washing machine and utility sink except I would send the sink drain p-trap out the back side of the wall instead of the way the pipe extends forward in Terry's photo.

    I'm hoping to hear some expert opinions on using the same drain for the washer and sinks placed back to back and thoughts on using a shower or tub drain as a floor drain.

    Thanks again.

    Linda
     
  10. geniescience

    geniescience Homeowner

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    ditto
    Location:
    humid summers hot, humid winters cold
    Utility sink is OK, with a washing machine. That is code. Sorry I didn't add this earlier.

    Now, would you want to re-interpret code so that two hand rinse sinks look like a utility sink? Hmmm. And would you be doing this with or without the blessing of your local authorities? Hmmm.
     
  11. geniescience

    geniescience Homeowner

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    ditto
    Location:
    humid summers hot, humid winters cold
    Shower drain = floor drain.

    Your tub drain has its P trap at the same place as these two above, so it is the same as these two.

    A floor drain should be primed.
    Search "trap primer" to learn more.

    If you hide the drain close to a wall or under a bench, it is easier for you to arrange for one of your existing drains to be primed from above. A pipe would carry some water to the drain. Then you wouldn't need to insert a primer line into the drain pipe.
     
  12. Linda49

    Linda49 New Member

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    Location:
    Texas
    Hi geniescience,

    I think I have completed all of your assignments, teach. I've been learning a lot. I have a real grasp on the fact that I know very little about plumbing drains and vents.

    Great info about the floor drain issue. I think the bathtub drain is in a good location for a floor drain. The sinks will be nearby so we can prime with a piece of tubing that will get buried in the floor when we raise it. Do floor drains come with an inlet for a priming tube? I don't remember seeing one on the ones I looked at at the big box stores.

    I tried and tried to use the washer drain for a shower with a trench drain, but there is no way I can do it and keep wheelchair turning radius everywhere. I have figured out a way to squeeze in my turning radius for the shower, sink and washing machine areas by making the toilet and shower a wet room with just a shower curtain between them. With this plan, I can keep the washer on its current drain, but I'd have to use a 45 to angle the standpipe back into the shower wall which needs to move about 4" back to the left of where it is in the second image.

    Any problem with putting a little dogleg in a standpipe?

    I'm not thrilled with keeping the washer and dryer here because they become the focal point of the master bath, but I guess I can build a cabinet around them. It will look like an entertainment center.

    Thanks again.

    Linda
     
    Last edited: Sep 1, 2010
  13. geniescience

    geniescience Homeowner

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    ditto
    Location:
    humid summers hot, humid winters cold
    Post your DWV sketch again.
    Master plumbers can comment next.

    Floor drains don't come with an inlet for a priming tube, as far as I know.
    A dog leg is an offset, already discussed above.

    /d
     
  14. Linda49

    Linda49 New Member

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    Texas
    d,

    My concern about the offset was specific to a washing machine standpipe. Since you said I may not be able to equate hand sink and laundry tub. Then considering the flow being more forceful on a washer drain than a sink drain, I thought maybe I had better ask about putting an offset on a washing machine standpipe before I proceed with designing that little jog back into the wall. I have since read a post by Terry in which he answered that it was within code to use a 45 to get a washer standpipe into a stud bay, so I think I'm good there.

    We don't want to do things that aren't to code, but we don't plan to 'fix' anything that has been working fine for twenty five years either. Much as I would like to swap places for aesthetic reasons, I guess I'll just keep the washer/dryer and sinks on the same drains and tweak the old floor plan by just turning the two fixtures 90 degrees to widen the room and create more wheelchair turning space. Function over form.

    I checked on the drain priming inlet. I found one in a fitting, but not in the drain itself. We may just go with the idea of putting mineral oil into the trap to prevent the water from evaporating. (I keep envisioning waterbugs crawling into the primer pipe and either clogging it or popping out the sink drain.)

    The next stumbling block is how to raise the toilet by an inch and a half and remove the offset flange so we can put on a new (and better constructed) offset flange that moves the toilet 1 1/2" or more to the right. (Center line is 13 1/2" from the side wall, and it really is too tight now. 15" is code.) We'll get a new 10" offset toilet, so we won't need an offset to the front anymore. I think that the fact that we are raising the floor an inch and a half is to our advantage when installing a new and better offset flange, but I am really worried about how we are going remove the old one and connect the new one within a concrete slab.

    I was considering a Caroma 270 toilet that can offset sideways, but I read that there is a splash issue, and it is very long anyway. I'd rather get a 10" Toto Aquia III and use an offset flange.

    I saw a video of a plumber drilling a closet flange out with a special boring bit, but then he used an inside flange that reduced the diameter of the drain pipe. I don't think I'd want to reduce the diameter AND offset at the same time unless we have a 4" pipe. I don't know the diameter yet since the throne is still in place, but I think it is 3" if memory serves. (Of couse, it rarely does).

    We looked at what the big box store have on the shelf last night. Inside 3", outside 3" pipe or inside 4" pipe, even outside of the 3" fitting and inside 4" fitting.

    PlumbingRough.jpg

    Thanks.

    All comments are welcome.

    Linda
     
  15. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    New England
    If you open the floor to install a new toilet drain and flange, you could easily move it to where you need and then use a 'standard' 12" rough-in toilet. That will give you many more options as well. Depending on which direction the pipe travels relative to the new, desired position, you may not need to break up much. You could get an idea once you pull the toilet to see which way the drain turns.
     
  16. Linda49

    Linda49 New Member

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    Location:
    Texas
    Hi Jim,

    Thanks for the suggestion. I doubt that there is enough pipe to add a new toilet drain because the toilet practically sits on the main lateral just inches before it exits the house to the septic tank. The perimeter slab beam has to be just on the toilet's left as well. In addition the sink drain must tie into the lateral at almost the same position as the toilet. So I'm thinking it is practically all fittings from the toilet to the main lateral, and all fittings around the toilet area on the main lateral. Even if we could find enough pipe on which to place a fitting, the perimeter beam or the sink drain fitting would likely stop us from getting into the right position to place that fitting.

    I think our only choice is to try an above slab replacement of the offset flange.

    Linda
     
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