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Thread: Wind draws water from toilet bowls

  1. #1
    DIY Junior Member SirElliott's Avatar
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    Default Wind draws water from toilet bowls

    As I write this the wind is blowing 30 to 35 mph with gusts to 57 mph. This is not uncommon here in the Cascades. Every time we get strong wind it lowers the water level in all of the toilet bowls.

    The other day I smelled sewer gas and went exploring, to find that the toilet bowl in the basement had lost its seal. This toilet is out of the way and doesn't get used much. So there may be 2 things going on, the lowering of the level and then evaporation of the small amount of water remaining.

    The house is new construction, great experienced plumber did the waste system. Three vent stacks, all on the lee side of the roof from the prevailing winds. The house has a conventional septic system.

    My biggest fear is being away for a week or two and having sewer gas fill the house.

    So what can I do to reduce the effect?

    My guess is there is a venturi effect on the vent stacks which creates a negative pressure and pull down the water level. I guess there could also be a positive pressure wave that creates a rocking effect in the bowls. It also might be both effects working together.

    I assume its happening with all the traps, but the floor drains have trap primers, so if there is activity they refill. Maybe it only is happening with toilet bowls because of their design

    Will putting a trap upside down on the top help?
    How about drilling holes in the stack above the roof.
    Would adding a double wye to the top of the stack help?
    How about extending the stack above the highest point of the roof?

    Thanks, Elliott
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    Last edited by SirElliott; 02-21-2012 at 05:24 PM.

  2. #2
    DIY Senior Member bluebinky's Avatar
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    At my Texas house, we occasionally get 70+ mph winds with no such problem. My guess is that the location of the vent is more of a problem than the geometry. Maybe another vent somewhere else would help?

  3. #3
    DIY Member kevink1955's Avatar
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    Is there a fresh air inlet on the house side of the main line trap, if not that's your problem. The roof vents need something to pull air from or they will pull down the toilet traps.

  4. #4
    General Engineering Contractor ballvalve's Avatar
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    A search for vent caps will solve any venturi effect. Or stick your Stainless steel potscrubber in the hole.

  5. #5
    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by SirElliott View Post
    The house is new construction, great experienced plumber did the waste system. Three vent stacks, all on the lee side of the roof from the prevailing winds. The house has a conventional septic system.

    My guess is there is a venturi effect on the vent stacks which creates a negative pressure and pull down the water level. I guess there could also be a positive pressure wave that creates a rocking effect in the bowls. It also might be both effects working together.
    Sounds like a form of venturi. Caps might fix it if it is just venturi (an effect of the opening itself), but I suspect the issue might be because the vents are on the lee side. The roof or any obstruction acts like an airfoil, reducing the local pressure on the back side. Meanwhile on the face of the house you have slightly elevated pressure that would add to the problem as you surmised. I'm not sure how plumbers account for this in normal layout of the vent stack. Extending the vent stack(s) some greater distance above the roof might solve the problem (and wouldn't be too hard to experiment with before settling on a final configuration.)

    I've seen some interesting venturi effects on process equipment and instrumentation, particular with decanters and VL separators. It can really mess with a DP level leg if the layout of the taps is not carefully considered. Most common result is incorrect level reading leading to two phase flow (L-L or V-L) out one end or the other. Relocating taps or enlarging process piping where the tap is usually fixes or at least minimizes the problem. The hard part is convincing operations folks or electrical engineers (instrumentation) that the readings they are getting are way off because of the bias of the venturi DP.

    Good luck and let us know what you find.

  6. #6
    DIY Junior Member SirElliott's Avatar
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    Quote Originally Posted by bluebinky View Post
    At my Texas house, we occasionally get 70+ mph winds with no such problem. My guess is that the location of the vent is more of a problem than the geometry. Maybe another vent somewhere else would help?
    Thanks for your suggestion. There are currently 3 vents. While they are on different roof sections, they are all on the lee side. I guess I'm leery of creating more roof perforations without confidence that this would solve the problem.

  7. #7
    DIY Junior Member SirElliott's Avatar
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    Quote Originally Posted by kevink1955 View Post
    Is there a fresh air inlet on the house side of the main line trap, if not that's your problem. The roof vents need something to pull air from or they will pull down the toilet traps.
    So how would you plumb that? The house is finished so we would have to open sheetrock unless your suggestion putting a vent in the main drain pipe where it exits the house but before the septic tank. That would put the vent downstream of the house trap.

    Would adding an air vent in a downstairs sink work? Isn't that what the stack is for?

  8. #8
    DIY Junior Member SirElliott's Avatar
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    Quote Originally Posted by Runs with bison View Post
    Sounds like a form of venturi. Caps might fix it if it is just venturi (an effect of the opening itself), but I suspect the issue might be because the vents are on the lee side. The roof or any obstruction acts like an airfoil, reducing the local pressure on the back side. Meanwhile on the face of the house you have slightly elevated pressure that would add to the problem as you surmised. I'm not sure how plumbers account for this in normal layout of the vent stack. Extending the vent stack(s) some greater distance above the roof might solve the problem (and wouldn't be too hard to experiment with before settling on a final configuration.)

    I've seen some interesting venturi effects on process equipment and instrumentation, particular with decanters and VL separators. It can really mess with a DP level leg if the layout of the taps is not carefully considered. Most common result is incorrect level reading leading to two phase flow (L-L or V-L) out one end or the other. Relocating taps or enlarging process piping where the tap is usually fixes or at least minimizes the problem. The hard part is convincing operations folks or electrical engineers (instrumentation) that the readings they are getting are way off because of the bias of the venturi DP.

    Good luck and let us know what you find.
    I'm leaning strongly to venturi but not sure if it is mostly on the stack outlet or the whole roof. If it is mostly venturi on the pipe, than drilling some air inlet holes below the opening should break the negative pressure.

    I am inclined to think that the roof itself is acting as a very good wing, compressing the rushing air as it reaches the peak, which would create negative pressure (lift) on the lee side. The only bug in that theory is that the center portion of the house is round. That roof has a cone shape and that stack is in the shadow of the cone but its not a very good airfoil.

    If the whole roof is creating a negative pressure then I doubt caps would have much effect. Makes me wonder if I can run a relief tube from each stack to the peak and then into the positive air.

  9. #9
    DIY Member kevink1955's Avatar
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    The fresh air intake needs to be on the house side of the main trap, I know mine is always pulling air in which rises thru the system and exits thru the roof venting. I am assuming this setup is universal in all parts of the country but am not sure. Around here if the main trap is in the basement the fresh air intake exits the building thru the foundation or rim joist. If an outside trap it comes out of the ground and is caped with a 180 degree bend so it points to the ground.

    What say the pros, Is this just a NY thing or is it used everywere and do you think not having a fresh air intake could put the system in a vacuum?

  10. #10
    Retired Defense Industry Engineer jadnashua's Avatar
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    Most homes do not have a main house trap...only the individual traps at the fixtures. You can't really suction a toilet trap dry easily, but you can rock the water back and forth, which will let some spill over the weir. Climbing up on a roof can be a pain and dangerous, but you could take a coupling and a section of pipe and set it on the existing pipe to extend it some to see if that would work. As long as you don't glue it, you can remove it later if it doesn't do anything. A couple of 90's hooked together to point it down might help, too as well as an air cap.
    Jim DeBruycker
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  11. #11
    In the Trades Plumber111's Avatar
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    He likely does not have a house trap, or as I call them, a professionally installed clog. If he has one, he should yank it.

    High winds within a "closed" system can create positive pressures causing the trap seal to rock and decrease the water spot, or even almost dry the trap.

    Trying to think of a legal way to correct it.

  12. #12
    In the Trades Plumber111's Avatar
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    I hate to suggest a maintenance item on something that should require no maintenance, but a Studor Filter may fix it on the right vent. And who knows, you may not have to maintain much at all. Maybe only when you have the roof worked on.

  13. #13
    Retired Defense Industry Engineer jadnashua's Avatar
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    A septic system needs an outlet, too...not sure an AAV would work for that. An AAV only lets air in, not out.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  14. #14
    In the Trades Plumber111's Avatar
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    Quote Originally Posted by jadnashua View Post
    A septic system needs an outlet, too...not sure an AAV would work for that. An AAV only lets air in, not out.
    Do a little more homework. I think you might change your conclusion. Not about AAV's, but my suggestion at Post 12. Read carefully....
    Last edited by Plumber111; 02-22-2012 at 08:11 PM.

  15. #15
    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by jadnashua View Post
    Climbing up on a roof can be a pain and dangerous, but you could take a coupling and a section of pipe and set it on the existing pipe to extend it some to see if that would work. As long as you don't glue it, you can remove it later if it doesn't do anything.
    That's exactly what I was envisioning. Bring pipe and some caps as well. Test a cap on one or two with and/or without the extension to figure out what works and what doesn't.

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