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fumes from sink, Double trapping?

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  • fumes from sink, Double trapping?

    Hello,

    I have a problem with sewer gases emanating from the bathroom sink. (more below)

    I am usually pretty handy and figuring things out but this has me stumped except for one theory. I have included a couple of photos for better understanding. For your reference, our home is a 2 story house in Aldergrove, BC Canada.

    Pic#1
    This is beneath the bathroom sink and as you can see it does have a trap. The pipe leads into the wall behind and straight down about 18" to Pic#2.

    Pic#2
    The pipe exits the wall and proceeds downward between the joists under the floor. As you can see, the tie down is bracing the pipe and measures approximately 6" at its lowest point from the underside of the plywood floor.

    Pic#3
    The pipe continues approximately 7' and drops another 6" to the connector that then takes a 45 degree angle to the main. It enters this picture from the top. The Main goes pretty much straight up to the roof for venting.

    Pic#4
    Here again is the Main showing the sink pipe entering the pic from the top left. The toilet from the same bathroom is the larger pipe entering the main from the left. On the right, you can see the trap for the tub.

    The tub and toilet do not appear to have any gases emitting from them.

    I have accessed the vent pipe on the roof and dumped a couple of gallons of water via a hose. There was no resistance. The smell emitting from it seemed to be identical.

    The only time the sink emits fumes is when the water is first turned on and if left on full-blast for at least 1 minute, the drain will eventually no longer 'stink'. At that point, I believe the gases have stopped.

    My Theory:
    Because of the long 7' straight section of pipe running horizontally with only 6" of drop, I think that this acts almost like a second trap. As water flows and fills this section of pipe, the gases stuck between here and the real sink trap get "trapped". As more water enters this area and can't flow out nearly as fast as it enters, it builds up pressure and forces the gases up and through the sink trap until completely evacuated leaving only water. In other words, Burp.

    If this is true, is it possible to remedy the problem by cutting back the junction located in Pic#2 and increasing the angle of drop to the Main?

    …or am I way off base?

    ...If I am correct, why does the gas burp rather be sucked down by the venturi effect? Is the water not moving fast enough?

    Thank you for any help.
    Attached Files

  • #2
    Re: fumes from sink, Double trapping?

    you may want to put a cup of bleach down the drain some night before you go to bed and see it will disinfect and clean your trap as the smell might just be crud built up in your waste! the typical slope for a sink drain is 1/4 inch per foot and from what you say you do have a bit much but it should not cause the trap to suck itself dry and cause the order problem you are describing. I still say add the bleach and see if that works.
    ________
    Dodge Ram Specifications
    Last edited by TOPDAWG; 02-24-2011, 06:03 PM.
    Mike

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    • #3
      Re: fumes from sink, Double trapping?

      Are you running hot water when you notice this problem?

      Run hot water in your kitchen, and other bathrooms if you have them. Do you notice an odor?

      Sounds like it could be the water heater to me.
      Proud To Be Union!!

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      • #4
        Re: fumes from sink, Double trapping?

        Originally posted by Aaron91 View Post
        Are you running hot water when you notice this problem?

        Run hot water in your kitchen, and other bathrooms if you have them. Do you notice an odor?

        Sounds like it could be the water heater to me.
        quit possible, He should check that as well
        ________
        CREOLE & CAJUN COOKING
        Last edited by TOPDAWG; 02-24-2011, 06:03 PM.
        Mike

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        • #5
          Re: fumes from sink, Double trapping?

          Check the pop up drain. Hair and soap residue can cause some bad odors.
          Buy cheap, buy twice.

          Comment


          • #6
            Re: fumes from sink, Double trapping?

            Guys: TOPDAWG,Aaron91,gearjunkie

            This is sewer gas not smelly crud beneath the drain.

            The sink drains very well and has no resistance (backup) with both hot and cold full on. And I have about 48lbs pressure last time I checked.

            It is not a clog or narrowing of passage.

            The Sink Trap does not get sucked dry. The only time we smell the gas coming from the sinks drain is when we turn on the water of periods of less than a minute or two.

            The test I ran was with COLD water only and this problem has absolutely nothing to do with the hot water tank.

            Thanks for each of your replies, Any other ideas?

            Comment


            • #7
              Re: fumes from sink, Double trapping?

              If it happens when the water is running i sure doubt that it is sewer gas you smell as the trap will not evacuate as the water is running into it.
              ________
              GRAND CHEROKEE
              Last edited by TOPDAWG; 02-24-2011, 06:05 PM.
              Mike

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              • #8
                Re: fumes from sink, Double trapping?

                Sounds to me like your trap goes into the wall and straigt down until it hits the stack and the only vent of the lav is from the main stack . which acts almost like an S trap as it is not vented until after it ties into the main stack. You might think about installing an air addmittace valve underneath the bathroom sink . That will eliminate the burping Isue and more than likely the oder you are getting

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                • #9
                  Re: fumes from sink, Double trapping?

                  I'm curious about what kind of glue your system was assembled with. ABS glue doesn't look white. It may be PVC glue or it may be 3-way cement, but I can't help but wonder if this job wasn't done by an amateur.

                  Comment


                  • #10
                    Re: fumes from sink, Double trapping?

                    have you physically taken apart the tailpiece and trap and cleaned them out?

                    Comment


                    • #11
                      Re: fumes from sink, Double trapping?

                      Originally posted by ridgidpipe View Post
                      Sounds to me like your trap goes into the wall and straigt down until it hits the stack and the only vent of the lav is from the main stack . which acts almost like an S trap as it is not vented until after it ties into the main stack. You might think about installing an air addmittace valve underneath the bathroom sink . That will eliminate the burping Isue and more than likely the oder you are getting
                      There is no breaks in the stream between the sink trap and the stack however; the stream flows from the trap, into the wall, straight down, turns just over 90 degrees, runs 7 feet and then takes another turn of nearly 45 degrees before it hits the stack. At no time does this pipe-line break the horizontal barrier.

                      The only vent is at the top of the main stack, yes.

                      I am unsure if a air admittance valve would work, isn't this a pressure and not vacuum problem?. Where would you attach it on to the pipeline?

                      I have included a diagram for better clarity.

                      Thanks
                      Attached Files

                      Comment


                      • #12
                        Re: fumes from sink, Double trapping?

                        Are you on Well Water or City Water?

                        Is this a second story bathroom?

                        Are absolutely sure your trap keeps water?

                        Do you know for a fact that once the drain under the sink enters the wall it is not attached to anything else? Have you opened the wall and looked?

                        The bottom line from an engineering and physics standpoint is its impossible to get sewer gas smell if what your showing in the pictures is true. You would have to vacuum gas through the trap while water was running. That takes positive pressure to achieve. The only way I could see that happening is if there was another line tied into the drain in the wall directly behind the sink.

                        The only other thing I could think of is water quality.

                        Comment


                        • #13
                          Re: fumes from sink, Double trapping?

                          Originally posted by Herk View Post
                          I'm curious about what kind of glue your system was assembled with. ABS glue doesn't look white. It may be PVC glue or it may be 3-way cement, but I can't help but wonder if this job wasn't done by an amateur.

                          Thanks for pointing that out to me, I hadn't noticed.

                          I have checked the whole stack and lines attached and this is the only line with this type (Hard & white) glue on it. Also I found a few BeaverLumber (an old hardware store in the area) sales stickers on them.

                          I think we can conclude from this that this line, although following the basic rules, is not done by a pro.

                          Check out the drawing I did.

                          Thanks

                          Comment


                          • #14
                            Re: fumes from sink, Double trapping?

                            i was was thinking if you have a second floor maybe that line for the lav goes straight up and is being wet vented to another fixture like the stack is , the waste rushing vertically down from the upstairs fixture might be blowing the trap seal

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                            • #15
                              Re: fumes from sink, Double trapping?

                              Originally posted by stokefire7 View Post
                              have you physically taken apart the tailpiece and trap and cleaned them out?
                              I am unsure which is the head or which is the tail, can you elaborate?

                              Besides, I don't get my hands THAT dirty, yuk.

                              I am researching for better understanding of the problem. We were told 'not to bother', but I cant stand to wash my face, and brush my teeth at a sink with this stink.

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