Help Please! Totos Back-to-Back Something Must Still be Wrong!

Discussion in 'Toilet Forum discussions' started by mbose, Mar 11, 2021.

  1. mbose

    mbose New Member

    Joined:
    Mar 11, 2021
    Location:
    Houston
    Slab-on-grade houses sink here in Houston, and we had a company raise ours and redo the underground plumbing. About a week after the work was done we noticed that flushing one Toto back-to-back toilet pulled water from the other. It doesn't matter which toilet is flushed, it happens both ways.

    Terry's YouTube video on back-to-back toilets was awesome and immediately identified the mistake our plumbers had made:



    PXL_20210123_151718935.jpg

    We showed the company the video and they researched it, pulled all the dirt back out, and redid the plumbing. To my eyes (that know nothing about plumbing) it looks like they did it the way Terry showed in the video:

    IMG_20210304_073326.jpg IMG_20210304_073442.jpg

    This change did not affect the toilets. Flushing one still pulled water from the other.

    Next, they suspected the venting. The new 3" vent they installed below ground connected to an existing 2 inch vent behind the wall. They opened the wall and cut the pipe so that the 3" vent was wide open about 18" above the toilet. Their goal was to give this maximum venting and see if it helped. They did not think the 2" vent was the problem, but it was worth a try even though we opened the wall to do it.

    PXL_20210311_151859093 (1).jpg PXL_20210311_151851751 (1).jpg

    This did not reduce the amount of water being pulled, so they reconnected the vent as shown in the photo.

    At this point they are stumped. I hope someone can suggest a next step.

    Thanks for any help in advance!

    Signed: Desperate to flush in Houston (still have a little sense of humor left....)
     
  2. Reach4

    Reach4 Well-Known Member

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    Location:
    IL
    Cool. How high?

    I have a suggestion for you if you are motivated enough. You can make an open-tube manometer with some cheap clear tubing and a glass jar or glass glass. That would read the water pressure on the other side of the water seal. It is not that hard once you get over the idea of threading a tube through your toilet trap.

    You can measure the air pressure at the far end of the tube. The procedure would be to run some clear tubing through a trap into the trap arm or past the weir in a toilet. Blow to remove any water in the tube.

    Take the near end, and put it into a glass of water. This glass could be elevated, maybe somehow taped into the soap dish. It could be low for better positioning for video. Tape the tubing to support that to keep the end of the tubing in place. If vented, the level of the water in the tubing should be about the same as the other water in the glass. If there is vacuum in the drain air, the water level in the tubing would drop relative to the level of the water in the jar.

    Clear tubing is pretty inexpensive . If you know somebody on oxygen that person probably throws away suitable tubing every month.
    You can thread the tube through a lavatory trap, if there is nothing blocking the way. You can shove the tubing through the trap of a toilet. Through the toilet would directly show what the toilet is faced with.

    There is an electronic manometer that could be used. However the open-tube manometer does not need calibration. The electronic one might be able to remember peaks however -- I never used one.

    So what do you do with the info? If there is vacuum recorded of more than 1 inch of water, that could explain the symptom. Why the venting is not sufficient to prevent a 1 inch vacuum would could be investigated. An AAV could supplement the real vent to prevent a 1 inch vacuum. An AAV cannot relieve a positive pressure, but a positive pressure will not suck water from a bowl. Houston code may prevent the use of an AAV, but an exception could be made for using one to supplement a real vent to the roof. You could find that the (3 inch?) vent path to the roof is obstructed, and be able to get that fixed.

     
    Last edited: Mar 11, 2021
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  4. Terry

    Terry Administrator Staff Member

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    The video explains why the water is being "pushed" out of the bowls, and not being "pulled" from the bowls.
    Water skips across the fixture fitting and air pushes the water upward in the bowl, which then slops over the high part of the trapway and down the drain. The instructions that come with Kohler and TOTO specifically say to use a wye fitting, and not a double combo or double santee fitting.



    [​IMG]

    A double wye, not a double fixture fitting or double santee.

    p507-030-3.jpg
     
    Last edited: Mar 11, 2021
  5. Jeff H Young

    Jeff H Young In the Trades

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    If I understand correctly the vent between 2 toilets was suspect and was 2 inch was increased to 3 inch and even with the vent disconected it wouldnt function proper? honestly i dont think increasing vent size "was worth a try" I think this rules out venting. maybe you got blockage in drain?
    Didnt see terrys post but agree and would have checked with toto since Im aware of back to back problems but not up on details. edited after terrys posting I think its clear now any doubt contact Toto
     
  6. Terry

    Terry Administrator Staff Member

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    The fix is to plumb one toilet to the vent with a santee and drop down with a long turn 90 to the horizontal. Downstream of that, add a wye pointing to the toilet on the right, and pick that up with a long turn 90. Because toilets are meant to siphon, that works. That is how many of us are now doing two toilets that close together now.

    Jeff, looks at my video that explains this. The water level rises each time. That isn't a siphon, it's the surge of air and water pushing the bowl water upward. This happens with toilets that flush quickly. The old five gallon bowls that slowly, slowly drained down didn't do this.

    A 2" vent is enough for two bathrooms. It wasn't the venting.

    dwv-2-toilets.jpg
     
    Last edited: Mar 11, 2021
    Tuttles Revenge likes this.
  7. Jeff H Young

    Jeff H Young In the Trades

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    Just wondering how you approach toilet replacements on existing back to backs when no other work is being done Terry? Avoid Toto brand completely? what about others w/c being considered? From the forum here If I get back to backs to change out I'm going to be on alert of this issue, actually I just did a back to back owner supplied and it worked out fine wasn't TOTO though some Costco called OVE I hated the install

    ove-decors-sabine.jpg
     
  8. Terry

    Terry Administrator Staff Member

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    I don't worry about it. You can see from the video how many flushes it takes to lower the bowl water. It takes a lot.
    Meanwhile...........I have great flushing toilets. The water left in the bowl always maintains the seal anyway. However, when I remodel the bathrooms, I will be changing the rough plumbing in the walls and fixing that.
     
    Jeff H Young likes this.
  9. Jeff H Young

    Jeff H Young In the Trades

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    Great Thanks for reply Terry A bathroom remodel takes on many meanings and on a slab I don't plan on doing much underground work if fixtures aren't moving and walls are staying put. On a crawler there are issues easier to address.
    Still gotta watch the video and hope that the OP mbose has got all his answers clear now!
     
  10. mbose

    mbose New Member

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    @Terry Thank you!

    I will pass this along. One question, is the current connector that they are using a WYE, or is it still just a double fitting fixture?


    IMG_20210304_073326.jpg
     
  11. mbose

    mbose New Member

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  12. Reach4

    Reach4 Well-Known Member

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    Ahh, makes sense. I was thinking you might be avoiding flood waters, and going up more.
     
  13. PlumbNuts

    PlumbNuts SC Licensed Plumbing Contractor

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    The fitting that you have pictured is called a double combination (a combined wye and 1/8 bend); but if you look at the horizontal line across the bottom of the two side inlets of the fitting you will notice that it is below where the top of the vent begins. Now if you look at the picture above of the double wye with the 2 street 1/8 bends added to creat the combination and follow that same line you will see that the water line is obstructed by the vent and does not allow the water to rush from one side to the other.
     
  14. Reach4

    Reach4 Well-Known Member

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    That is a double fixture fitting. Terry showed a double combination in post #2.
     
  15. PlumbNuts

    PlumbNuts SC Licensed Plumbing Contractor

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    Yes, I worded it wrong but I was trying to explain the differences between the two so that he could understand why that was happening.
    Thanks for catching that and keeping it from confusing him more.
     
  16. Terry

    Terry Administrator Staff Member

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    Water will skip across a double fixture fitting, with water running over to the other side, which forces the water in the bowl to rise and then slop over the top of the trapway. You lose a bit of water each time this happens.
    I noticed the first time in 2000 when I had a toilet lifted and while in the bathroom, someone flushed the toilet in the other bathroom. I saw water rushing up and making a "hey buddy, lookie at me" sort of sound. I ran into the next bathroom, and said, "Did you just flush a toilet and cause water to skip across the double fixture fitting on purpose?" Or were you just doing your business. Anyway, the moral of the story is, don't use a double santee, don't use a double fixture fitting, just don't.
    Either that, or quit worrying about it. Dooh!
     
    Jeff H Young likes this.
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