Odor from bathroom septic system. Multiple plumbers have been stumped

Home was built in 1988 with septic system. Odor coming from 2 of the bathrooms and back access to a tub in another bathroom. All new toilets and wax rings put in. Septic tank cleaned and working fine. Vents were snaked from the roof access and showed no leaks or cracks in pipe. I even ran a garden hose thru the vent on the roof to see if any leaks came thru the walls (to see if there was a small crack). The odor comes and goes and is worse if both tubs have been used and worse if it rains. Sounds crazy, but I need a solution. I have had 5 plumbers come out and no answer. We have made the under sink pipes larger, cut holes in the walls to check the pipes. All toilets and drains work properly
Please does any one have any solutions or suggestions? I am out of ideas.
  13 answers
  • I had this issue with a client several years ago. This always happened when the air was really damp outside. Dry days not even a slightest odor. Turned out that there was air currents off of the roof that caused the odors to flow down and back into the house. They solved the issue by installing a special venting device that allowed air in, but not out. A check valve for air of sorts. You can confirm this quickly by placing a upside down metal coffee can on the main vent. This should still allow air to enter enough so things still flush properly. Wait a few weeks through different weather and see what happens. If it goes away you can install this air trap, or have the plumber raise or relocate the vent pipe to another location. It is unknown why this just starts after many years of not having issues. But it does. It can be from anything from cutting down a tree, to trees growing taller, to changing something on the house or anything that can change the way the air flows around the home.
  • Lori Shaneck Lori Shaneck on Oct 30, 2014
    have you tried changing out the wax seal under the toilets? ours backed up a few years ago and we couldn't get rid of the smell either, until a friend told us that wax will hold the smell(think candles)
  • Denise Denise on Oct 30, 2014
    Hi Thank you, yes we have changed them multiple times tried various brands no luck.
  • Denise Denise on Oct 30, 2014
    Thanks for the answers, but I'm still hoping for more ideas. Thank you for the idea to try the denture tablets, you should have seen the looks I got when I cleaned the store out of denture cleaner. I tried it today in all the toilets, sinks and tubs in the bathrooms that have the odor. I am keeping my fingers crossed.
  • Enjb Enjb on Nov 02, 2014
    You need to have the outflow to the septic tank checked. I had the same problem and the line from the house to the street side sewer was cracked and collapsed. Yours might be collapsed from the house to the septic tank.
  • Do not waste any money or any more time until you temporally cover the main vent with a can. You can use aluminum foil also and a large rubber band. punch just a few holes in it. Not to many. Remember however as the weather begins to go below freezing you must remove any cover or the pipe will ice up from the steam that flows upward and out. That is why the main is always 4 inches wide. Anything smaller and in severe cold weather the pipe will begin to ice up until it closes all together. But cover and leave for a few weeks to see if the smell goes away. I am 99% sure it will do the trick.
  • Denise Denise on Nov 02, 2014
    Thank you for the tip. I will try to cover it today. Wouldn't this cause the odor to be trapped in the house and the odor to be worse? I thought the vent was where all the odor was released? I also think it is really strange that the odor is only in a few bathrooms not all of them.
    • @Denise no it will not. Its all about the heavy outside air. Some how it makes it into the house and based upon where the vent is it is appearing to come from the bath areas. Odors caused by plugged septic systems can be found by simply walking around the outside of the home. Backups will come up to the surface where the odor come from. Plugged or damaged field pipes, diverter boxes, or any of that will show up as back ups in the lower levels of the home or out any vent that is installed pre septic system. Unless the traps are being pulled dry from insufficient venting, there is no way at all for any odors to come into the bathroom from the sinks, showers or tubs. When you flush toilets do you hear a gurgling sound in the sinks or tub? If you do that's the air trying to get into the pipes as the water runs down the drain from the toilet. If your not hearing any noise odors can only come from two other places, One you already checked which is the wax ring, the other is the vent pipe on the roof.
  • Colleen Colleen on Nov 02, 2014
    Not long after our house was finished and we moved in, I started noticing, at odd times, septic odor in the house. It was eventually discovered that at the point where the inlet pipe from the house meets the tank, or somewhere in that distribution box (I don't recall exact details), there was supposed to be some type of valve flap that opens and closes as necessary, that would block off odors from backing up into the house. This was missing in our tank. Have you had your septic service investigate the tank itself? Best of luck in sourcing the problem. I know how awful this is.
  • Denise Denise on Nov 02, 2014
    Thank you for the info. Who would look into that the plumber or the septic cleaner guy? Did you have the smell in all the bathrooms or only a few? My issue is only in 2 certain bathrooms and the area never changes. It seems that if the flap wasn't working the odor would be in all the bathrooms so frustrating! ty
  • Colleen Colleen on Nov 02, 2014
    It was a general odor that would originate in the basement near the outlet piping, and waft up through the entire house and would only happen intermittently. I would recommend you get someone who specializes in installing/servicing septic tanks to come investigate. The plumber won't want to get 'down and dirty' in the tank itself, lol. May be worth a try. It could very well be an issue with the tank or something more external to the house, especially since they can't find a problem from within.
  • Denise Denise on Nov 03, 2014
    someone recommended taking a air compressor to the lowest point ( in the basement) and putting a hole in the vent and blowing the vent to get whatever is stuck out any thoughts on this?
  • Do not use air at all, it can blow out wax ring seals on toilets if the stack is plugged. If the stack vent is plugged, which I doubt, the way to tell is to flush the toilet and listen for gurgling sounds from the sinks. If the stack is plugged as the water rushes down the drain, air must be pulled in behind it in order for the water to correctly flow. If the vent is plugged the traps in the sinks and tubs will be sucking in air to allow for the main drain to empty. Kind of like the water cooler in the office. You drain out some water and you get those bubbles filling the bottle. Well those bubbles is the air being forced down around the trap making that noise. If you do not hear that sound its unlikely you have a vent issue other then the odors dropping down around the house from the roof vent. Odors that originate from septic systems are caused by clogged drainage fields and such, This odor will be strong when walking around the home, it will not settle in the few rooms where your having an issue. If you do suspect the vent, have a plumber scope the drain vents and drains out to the septic if you want to put that to rest. But I still think its the heavy air outside allowing the odors to drop down right around the area of the baths.
  • Sandra Sandra on Dec 01, 2014
    Hi, we don't have a septic tank but we have had the same problem with odor coming from the shower in the guest bathroom where the shower is never used. The plumber explained that whatever it is at the top of the pipes coming up to the floor drain gets dried out from lack of use and causes the odor. if this is the case in your bathrooms with odor, all you have to do is pour a glass of water down the drain periodically, say once a week or every two weeks. Hope this helps.