A couple problems with newly installed back to back toilets

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by BrianInStL, Apr 7, 2014.

  1. BrianInStL

    BrianInStL New Member

    Messages:
    2
    Location:
    St. Louis, MO
    Hi guys, first off - great forum! I've browsed many times for various tips and it's a goldmine.

    On to my situation - Recently I installed 2 American Standard Mainstream 1.28 GPF toilets in my home. I know they are just about the cheapest toilets out there but I was just doing a quick remodel because I'm selling the home soon hopefully. My bathrooms and toilets are back to back.

    First and biggest problem - When I flush one toilet the other experiences a decent water level drop in the bowl. It's bad enough that if I use one toilet a couple times then the other has to be flushed BEFORE using if you plan on going #2 if you know what I mean. The water level is already pretty low being a 1.28 GPF toilet so this is a big annoyance. This happens to both toilets.

    From searching the forum a bit it seems it could be one of two problems - a clogged vent or a sanitary tee that lets water flow to the other side partially emptying the other toilet. I climbed onto my roof to take a look into the vent and flushed it out with a water hose - based on what I can tell it's not clogged. Now as far as the sanitary tee I do have one as you can see in the picture I attached but with there being a vertical drop of approximately 18-20" and then about 32" between the 2 toilet drains could the flushed water really make it all the way up to the other toilet? Are there any other suggestions as to what the problem could be? The old toilets didn't have this problem - I'm not sure of their age but would guess they were at least 15 years old.

    My second issue it that one of the toilets seems to drip into the drain randomly. This happened both when it was the only toilet installed (while second bathroom was being renovated) and continues to happen now that both are in. It happens whether or not the toilet has been used recently and also while it is being used. I have tank level set to spec and it seems like the flapper is seated correctly. The water in the bowl and tank doesn't seem to drop much when it happens and the toilet never "kicks" on to refill. Sometimes it's a slow drip and sometimes it can be a pretty constant dribble. Maybe it's more of an annoyance than anything but does anyone have any ideas as to what the problem could be? The second toilet does seem to do it for a few seconds after flushing but I think that's normal right?

    Any suggestions are welcome!

    Attached Files:

  2. wjcandee

    wjcandee Wise One

    Messages:
    1,936
    Location:
    New York, NY
    Well if you are flushing one and the other drops, and you can prove that the drops happen contemporaneously with the flush, then -- YEAH -- it's your setup. Since the roof vent is clear, then the answer is that the other toilet is creating a suction on the other side and siphoning some water from the bowl. Entirely-plausible. And isn't your roof vent being clogged.

    Don't guess about the leaky toilet. Check it with one of two methods. Either (a) close the water supply to the toilet, mark the tank level, and come back in 3 hours. If it's below the mark, you have your answer, most likely a leaky or non-seating flapper (or a cracked overflow riser); (b) drip some food coloring in the tank (I love this suggestion as if everybody just has it lying around), if it propagates to the bowl, then you have a little flapper leak.
  3. Reach4

    Reach4 Well-Known Member

    Messages:
    2,656
    Location:
    IL
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,045
    Location:
    Cave Creek, Arizona
    A properly installed vent between the two toilets SHOULD prevent a siphonage from occurring, regardless of which fitting, (and technically, neither of the ones in the photos is the "right" fitting), is used. Water "splashing" across the fitting would fill the bowl, not empty it. If the siphonage is created by the water flowing quickly past the toilet's opening, that is caused by the Bernoulli Principle, which a "central vent" cannot control, but neither would changing the fitting.
  5. BrianInStL

    BrianInStL New Member

    Messages:
    2
    Location:
    St. Louis, MO
    Thanks for responding.

    As far as the dripping I have been meaning to test using those methods, just been a little lazy. I'll try to do it today and report back.

    Now with the siphonage if it is suction causing it and changing the fitting to the double combination wye won't solve it then what next? I saw a post with a similar situation - the solution was a single wye was installed to drain each toilet and one of the toilets had to have a separate vent installed that then tied back into the main vent higher up. That would probably be too high of an expense and would require me tearing out walls that I just put in. Any other suggestions? Or should I just live with it?
  6. DaveHo

    DaveHo Member

    Messages:
    53
    Location:
    SE PA
    My take on it, the vent looks undersized. New toilets which use less water tend to evacuate the bowl quicker thus needing more airflow from the vent. Yours can't supply it, so it's suctioning water from the other toilet. Swapping the double sanitee for a double combo might help, or it might not. I'm not a pro, so don't take my thoughts as gospel.
  7. Terry

    Terry Administrator Staff Member

    Messages:
    15,298
    Location:
    Bothell, Washington
    This answer is wrong. :(

    The water from the opposing bowl is not being siphoned out.
    As water jumps from one arm to the other, it displaces air. It pushes air up into the opposing bowl. When air comes into the bowl, it raises the water level, and when that happens, the water then slops over the dam, the highest point of the trapway, and down the drain.

    I am waiting for the rest of the plumbers to figure out this simple problem.
    I'm waiting for the plumbing code to be re-written to solve this very simple issue. Both Kohler and TOTO are aware of this, I'm aware of it, and bit by bit, plumbing inspectors are being asked about it.

    Cut out the double santee.
    Replace with a double wye fitting. You don't want any water going up the other arm.
    A double fixture fitting won't work either. It's not as bad as the double santee, but it's also not the solution. It also allow "water skip", which pushes air into the other bowl, thus slopping water over the trapway dam, and lose of bowl fill.

    For venting, the 2" is fine. It's not the vent.

    [​IMG]

    A double wye fitting on the left is okay
    A double fixture fitting is marginal, it will still lose water in the bowls.
    A double Santee on the right doesn't not work well at all.
    Last edited: Apr 9, 2014
  8. Jacky1eye

    Jacky1eye New Member

    Messages:
    1
    Location:
    California
    2) 3 X 4 closet bends entering into a 3X4X2 santee. 4" closet flange, 3" water closet, 2" vent 4" receiving stack.
  9. Terry

    Terry Administrator Staff Member

    Messages:
    15,298
    Location:
    Bothell, Washington
    Jack,
    That's pretty much what he had, and that was causing probems. Repeating the the issue by installing a similar fitting, a fitting that both Kohler and TOTO in their instructions warn against, is not the fix.
    If you have a toilet from the 80's, then the old way works. This is 2014, and times have moved on. It's time to get into the 21st century.
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