Toilet bowl empties when flushing another (back-to-back) toilet

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by Emily Paxon, May 7, 2012.

  1. Emily Paxon

    Emily Paxon New Member

    Messages:
    5
    Location:
    Minnesota
    I have replaced to old model toilets with Kohler Cimarron 1.28 gpf using the existing plumbing. The toilets are installed back-to-back. When I flush one toilet, water is sucked out of the other toilet bowl. I have a 2" vent and appears to be clear. I'm wondering if something different needs to be done with the actual plumbing drain lines to accomodate these newer toilets. We did replace the copper with PVC but the configuration stayed the same.
  2. Cookie

    Cookie .

    Messages:
    5,660
    Location:
    .
    How do you know without a doubt the vent is clear? Also, did this happen with the old toilets and/or, did you ever see the water in the bowl move when someone flushed the other toilet?
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,804
    Location:
    New England
    Hopefully, you got some money back when you recycled the copper!

    The newer toilets flush faster than the old ones, and require a proper fitting in the wall. It must be a double combination wye, NOT a double sanitary T or sanitary cross. Otherwise, flushing one can shoot to the other side and create problems as you've discovered. A wye turns the waste at a 45-degree angle down, whereas the sanitary cross, you can basically see from one side to the other. The wye directs the water down with no chance of it shooting to the other side.

    [​IMG]
    Last edited by a moderator: May 7, 2012
  4. Terry

    Terry Administrator Staff Member

    Messages:
    14,763
    Location:
    Bothell, Washington
    The water sill skip across and creates a wave of air that forces the water higher and then as it recedes, goes down the drain. The newer toilets with the large flush valves can do this on some back to back fittings.
  5. Cookie

    Cookie .

    Messages:
    5,660
    Location:
    .
    Jadnashua,

    Are you saying that what you described can cause siphoning because that is his problem?
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,804
    Location:
    New England
    If vented properly, no, it isn't siphoning, but if you 'rock' the boat, some will end up going down the drain as the water shoots across, sloshing the water back and forth. The wye's shape prevents it from shooting across, and means you could actually run a snake down there if you wanted to (otherwise, it would likely just go out the other toilet).
  7. Emily Paxon

    Emily Paxon New Member

    Messages:
    5
    Location:
    Minnesota
    Thanks. This may be the problem. Just looked at the plumbing and it appears I have the tee/cross rather than the Wye. The toilets were installed just about a week ago and the vent was not plugged at that time. So, I'll check out this solution.
  8. Emily Paxon

    Emily Paxon New Member

    Messages:
    5
    Location:
    Minnesota
    In your opinion, will this problem be resolved by switching from the tee/cross(which I have installed) to the Wye?
  9. Emily Paxon

    Emily Paxon New Member

    Messages:
    5
    Location:
    Minnesota
    New to this forum and not exactly sure how to post a reply! I do have the tee/cross and not the wye. Hopefully by changing this the problem will be resolved. Thanks!
  10. Emily Paxon

    Emily Paxon New Member

    Messages:
    5
    Location:
    Minnesota
    Do you think replacing the tee with the Wye will solve the problem?
  11. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,252
    Location:
    Cave Creek, Arizona
    The "double combination Y-1/8 bend" is NOT an approved fitting for back to back installations either. Its construction, since the connections are at 45 degrees, creates TWO "3/4 S traps". The proper fitting is a "back to back fixture fitting" which is an amalgum of 30/60 bends raising the center lines to the point that "S" traps are not created. AND, it is shorter "face to face" so it fits into the installation better.
  12. Cookie

    Cookie .

    Messages:
    5,660
    Location:
    .
    I guess the big question here is, is the water in the bowl siphoning or is it rocking?
  13. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,804
    Location:
    New England
    Rock a cup of water, and some eventually will overflow...you'll end up with less water there. Direct a jet of water there from a hose (pipe) and most of it may end up down the drain.
  14. ramsey76

    ramsey76 New Member

    Messages:
    6
    Location:
    Massachusetts
    TOTO back to back install

    I went to purchase a Toto Clayton today from a local dealer and I ran into an issue at the end of the sales process.

    The sales rep / consultant asked me if the new Toto toilet is replacing an existing unit that is back to back with another toilet


    I said yes, and this my be a problem because of the G max feature of the Toto. The concern is that the Toto may draw water from the other toilet every time the Toto is flushed if a Tee connection was used to connect the two toilets in the intial installation.

    ( the house was bulilt in 1990 in and is in Massachusetts)


    My understanding is that a double Wye connection is ok


    Is there a way to get some insight into what type of connection we have with out ripping open a tile floor or gambling on buying a toilet ?



    Thank

    T
    Last edited by a moderator: May 25, 2012
  15. Terry

    Terry Administrator Staff Member

    Messages:
    14,763
    Location:
    Bothell, Washington
    You can pull one toilet, and then flush the other one. If you see water skipping across and coming up the other arm, then your fitting is allowing water across.
    I have something similar in my home, and yes, it will lower the water in the bowl some. It's not a big deal.
  16. ramsey76

    ramsey76 New Member

    Messages:
    6
    Location:
    Massachusetts
    Terry

    Thanks for the input

    If I replace the second toilet with a Toto G max model, will that make the problem worse


    I realize I may a draw on bothn toilets, but besides that any other issue

    [​IMG]
    Last edited by a moderator: Dec 19, 2013
  17. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,804
    Location:
    New England
    Pretty much any new low-flow toilet works because it starts the flow by moving the water faster through good design. So, it is not a problem unique to Toto, but would be true with nearly any brand.

    When you do flush a toilet, it assumes that it is starting with the designed level of water in the bowl. If, for some reason, the level was reduced (depends on how much), it may not flush well and require a second cycle (the first refill resets the bowl water height, the second does what the first would have done had it started full in the first place).

    how much, if any, of a problem it might be varies from none to annoying depending on exactly how yours are connected, the distances, and the piping layout.
  18. A.J. Gross

    A.J. Gross New Member

    Messages:
    1
    Location:
    Aberdeen, WA
    Toto drake causes a "fountain effect" in toilet of adjasent bathroom.

    We really like our new toto drake toilet, however it has created a problem for us. When flushed it causes a bubbling and splashing in our other toilet

    in our master bathroom. The toilets are back to back with a wall between them. We can also hear gurgling and sometimes see a splash in the master bath shower.

    Is there a plumbing answer to our dilemma? This was never a problem with the toilet we had before the Toto. Thanks, A.J.
  19. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,804
    Location:
    New England
    Toto warns that, because of the high water velocity, if the proper fitting is not in the wall, you can get water shooting across. This is true with most newer, water saving toilets and is not unique to Toto. The older toilets flushed slower, and you could get away with the fitting in the wall. It's likely you won't fix it until you tear the wall apart to put in a new fitting. This has been discussed a lot...use the search function.
  20. Pete@miramar

    Pete@miramar New Member

    Messages:
    1
    Location:
    duxbury ma
    Has there ever been a retrofit solution to this problem? I have 15 toilets with this problem with the drains in a concrete slab and 15 more on the second floor. Maybe something that involves cutting into the wall and sectioning out a piece of the vent stack and putting some kind of divider down into the cross tee to deflect the drain flow.
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