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Troubleshooting plumbing vents: this article describes how to examine the building's plumbing vent system piping and connections in order to diagnose, find, and cure odors in buildings including septic or sewage or sewer gas smells or plumbing drain and fixture noises that may appear indoors or outside. Here we list common causes of plumbing problems related to improper plumbing vents. We describe how to track down and correct these "gas odors" in buildings with a focus on homes with a private onsite septic tank but including tips for owners whose home is connected to a sewer system as well. What makes the smell in sewer gas? Sewer gases are more than an obnoxious odor. What causes that gurgling noise in a sink, tub or shower drain, and why do some fixtures "gurgle" when a toilet is flushed nearby? Here are the answers.
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Plumbing Vent Piping Defects May Cause Drain Noises or May Release Dangerous Sewer Gas Odors Indoors
Our page top sketch of a plumbing stack vent and other sketches included below are provided courtesy of Carson Dunlop Associates.
Details about plumbing drain line venting can be found at PLUMBING VENT DEFINITIONS & CODES, where we describe plumbing vent sizes, routing, clearances, and connections.
Plumbing noises: At PLUMBING DRAIN NOISES we explain the basics of proper plumbing vent piping and how errors cause trap siphonage, odors, and noises. We discuss how to diagnose and cure drain sounds (gurgling, bubbling, smells, poor drainage) at PLUMBING DRAIN NOISE DIAGNOSIS (gurgling drains means bad vent piping or clogged drains). Other advice about controlling plumbing noises in buildings is at SOUND CONTROL for PLUMBING.also PLUMBING VENT DEFECTS & NOISES and at CLOGGED DRAIN DIAGNOSIS & REPAIR. We discuss plumbing fixtures, such as loose toilets, as sources of sewer gas odors separately at PLUMBING FIXTURE TRAPS.
Plumbing drain or sewer gas odors: If you smell sewer gases in your building conditions could be dangerous (risking a methane gas explosion) or unsanitary. Also see Remedies for Sewer Odors and see ODORS & SMELLS DIAGNOSIS & CURE for advice on finding the source of smells or odors in buildings.
Because sewer gas contains methane gas (CH4) there is a risk of an explosion hazard or even fatal asphyxiation. Sewer gases also probably contain hydrogen sulfide gas (H2S) In addition some writers opine that there are possible health hazards from sewer gas exposure, such as a bacterial infection of the sinuses (which can occur due to any sinus irritation).
Depending on the sewer gas source and other factors such as humidity and building and weather conditions, mold spores may also be present in sewer gases. Also see Wet Weather or Cold Weather Septic Odors or Sewage Odor Diagnosis & Repair Guide for additional odor tracing and cure advice for odors occurring during wet or cold weather.
Troubles and mistaken sewer gas odor-sources along the way to finding this plumbing vent sewer gas leak problem included
Frequently Asked Questions (FAQs) about troubleshooting plumbing drain waste vent system noises & odors.
Question: what is "short stack" plumbing ventilation?
short stack ventilation? - John
John if you are referring to plumbing vents that are too short, we discuss that in the article above. I'm unsure what else you're asking. If a plumbing vent stack is too short a risk is that in climates where there is snow cover, under heavy snow conditions the vent may become blocked.
Question: unused plumbing drain now seems to be clogged
after noticing a standing water in a newly installed vanity - the drain hasn't been used for long time - I tried to used water pressure to dislodge any obstacle there. Instead I got a leak around the vent in the ceiling of the adjacent closet. Any comments? Thanks. - Ad
Reader comment: It sounds like your blockage is downstream and by using water pressure, you are pushing the water upstream toward the vent. There should not be any water in the vent pipe. - reader B
Question: faint sewer odors come and go in several areas of our house, worse towards septic tank
We notice faint odors that come and go in a couple of areas in our house. they happen to be closest to the end of the house where our septic tank is located. One distinct location is a bathroom where a toilet had previously been lifted by a plumber to remove a flushed toy and I am now suspicious that this wasn't sealed properly when replaced (how do I know if this is the case?). The other is an adjacent bathroom where a shower drain seems to smell despite regular addition of water - also notable is that this bathroom had a very pungent gas odor when the septic tank was pumped. Is it normal for odors to come back into the house during pumping? (or does this suggest a malfunction of the shower trap or possibly a ventilation leak?)
A plumber has suggested that the vent stack for this bathroom has been placed improperly on our flat roof, too close to a parapet (actually only 2 to 3 inches away)& that we are probably having downdrafts into the ventilation pipe (although I am not sure how this could explain the substantial flow of odor into that bathroom during pumping). The last area is in our garage where there is a utility sink & this also had a horrendous odor during the pump out. Oddly, these 3 problematic areas are in very close proximity to each other at one end of our ranch style house and I am not sure if there is a common problem between them or multiple separate problems. I have had it looked at by septic companies and plumbers and have not really gotten a solution. How do I find someone that can solve this mystery? - Arizona
Reply: use a smell patch test or a person with good sense of smell to track down strongest odor source, check toilet wax ring
Question: long horizontal plumbing vent runs can leak into ceilings below
One potential issue that was not mentioned in the article:
I cut-out and replaced the split section, but it appears that I need to modify the horizontal run so it has some slope on it to allow the rain water to drain out. Just an FYI for folks out there. - Mike T
Thanks Mike. - DF
Question: sulphur smell in closet adjacent to a toilet/bathroom
We have an issue with a sulfur smell in a closet on the second floor of our home. The closet shares a wall with the toilet in the bathroom. The bathroom and toilet do not smell, but there is a strong sulfur smell in the closet that comes and goes - it seems to be stronger on sunny days. There is also a window in the closet and a soffit vent right outside of the window. We had the plumber come out. He said he checked the vents in the attic and they were connected properly? Any ideas? Thanks!
Sulfur smells that seem to relate to a septic system or plumbing drains are often traced to a loose toilet, missing or leaky toilet wax ring, dry plumbing traps at unused fixtures, inadequate plumbing vent piping by location or routing, or on occasion, a loose leaky connection in the plumbing vent piping as it runs concealed through building walls, floors, or ceilings. If checking the easy accessible problems like toilet wax rings and dry plumbing traps doesn't solve the problem, and if you believe the plumber's view that all of the drains have adequately located and sized plumbing vent piping, then next might be a pressure test of the vent system to see if you can prove that it is leaking.
Question: when toilets are flushed sewage comes up in the bath tub, and toilets over-fill
I have 2 toilets that when flushed drain into the bathtub. I have a septic tank that has been checked and is working ok, Per the repair guy. We have had 3 separate plumbers come out and no one has been able to fix the problem. Toilets overfill with water by themselves, and when running anything like a dishwasher or Washing Machine everything overflows into the tub.... any suggestions?? I'm dying here.. - Shaun
Shaun I read more than one problem here:
1. your toilets over-fill: if you mean that the toilet tank becomes too full, that's not a drain waste vent problem, it is a toilet fill or flush valve control problem; if you mean that the volume of water in the toilet tank is normal (fills to the "fill line" marked in the tank) but the toilet bowl becomes too full when the toilet is flushed then
1.a. the toilet drain is clogged somewhere in its routing
1. b. the toilet drain is not properly vented and the result is slow draining
2. the toilet flush water volume and delivery rate is improper - check the flush valve
The observation that the toilets overfill and that "everything overflows (presumably backs up into) the bathtub when a dishwasher or clothes washer is running is a very strong indicator that you have a blocked or partially blocked drain. Sometimes the blockage can be pretty far downstream from the toilet(s) or even from the building itself. A clue that suggests that condition is that when no water has been run for 4 hours or more, you get a few good toilet flushes before things begin to back up (you're filling up the drain piping with wastewater).
If the toilets back up immediately, any time, regardless of how long since any water was run into the drain system, then the blockage is probably closer to the fixtures.
Question: toilet drains slowly - a 20 ft drain auger doesn't fix it, other toilets drain OK
I have one toilet that has been draining slowly, I have used a 20 ft plumbers auger and it is still draining slower than normal..the other toilet drains perfectly...? - Frank Mann 1/18/12
Frank, your question suggests that either your snake passed right by a partial drain blockage, the toilet is not adequately vented, or the blockage is further downstream in the piping but ahead of other toilets that are draining OK.
Question: double sink drains slowly
I have a double sink that was installed as part a renovation. When water drains in one sink, you hear a glub, glub, ..... coming form the other drain. I suspect the new installation was not vented properly. How can a positively identify the source of this annoying problem - Scott 3/19/12
Scott I would start by removing, cleaning, and inspecting the drain traps below the two sinks; also, if the sink is not properly vented, it would be common for the draining sink to draw air in to the drain pipe system through the adjoining sink drain opening and trap.
Question: black specs on bathroom sink keep returning
Two sinks in separate bathrooms have black specs around the sink bowl drain. If I clean them with bleach, or Comet within short order they come right back. I suspect it is coming out of the drains as the black gradates from darker around the drain to lighter a couple of inches out. The problem seems to increase in warmer weather. I am thinking mold, but the cause? I have tried dumping drain cleaner down the drain. I have also tried bleach at different times and it's a no go. Help me! - Tim 3/24/12
Tim I am doubtful that black specs on a sink are being caused by gases coming out of the drain, more likely there is a stain source in the water supply or plumbing system.
Question: open 4-inch vent found in basement, sewage has come out into the house. Can I just cap the vent?
To my horror I discovered an open 4" vent in my basement today, where some waste had poured out. We have an 1885 house and a lot of plumbers here over the years, this may have been hooked up to a commode years ago, who knows? In any case, if I put a no-hub cap over the open vent should that be ok? - Open 4" vent in cellar 5/15/12
Open, you can cap that unused vent line, but you also need to clean and sanitize the area where there was a sewage backup.
Question: Infiltrator brand septic system failure report 15 months after new
We've been in our house 5 years, it's got a septic system with those "Infiltrator" brand chambers in the leach field versus stone-and-gravel.
The leach field was brand new when we moved in; 15 mos. later, failed, and the original engineer came out and raked out the lines and installed an air vent in the lawn(he'd never put one in to begin with -who knows why!); and said we were good to go; he said it had not been aerobic from the get-go, hence a biomat buildup in the lines. We're super-careful of water, use Scot tissue brand, HE washing machine, all the right things.
Well lately, maybe past 6 mos., I've noticed in one place (happens to be front or side of house, in front of or to right of vent pipe on top of roof), slight septic smell when something's being used (dishwasher ...toilet got flushed ...shower running - - not just running water in a sink, but those bigger things). I have really really checked and it's not coming from anywhere inside our house, or near the septic cover in the grass, or in/on the lawn over the leach fields. It's just "in the air" right near the front/side and only when the water's going into the system. It dissipates within minutes after the flow of water into the system is over. Does it sound ominous or within the range of normal? - Margaret 5/9/12
Margaret from your note I'm not sure the problem with the system has been correctly diagnosed and repaired. A lot depends not only on the choice of septic components but how correctly they are installed. But I agree that you should not be smelling sewage. Ask the designer/installer to come by and make a more careful diagnosis and let us know what you're told.
Question: sewer smell in bathroom, plumber warns about drain layout
I have a sewer gas smell in bathroom, coming from around toilet and sink. Plumber said both sink & toilet are sharing a drain pipe & vent pipe. Also the toilet was moved about 8' from vent pipe by previous owners. Does this sound reasonable to you? Had septic tank pumped and it was all good there. The smell is worse on very humid and/or rainy days. - Etha 6/24/12
Etha, I think your plumber was warning you that the distance from plumbing fixtures to the vent may be a bit much and may result in inadequate venting.
Question: does it make sense to use a smoke test for plumbing vent leak detection?
We think we have a sewer gas problem in a one story house with one bath, a kitchen, a dishwasher, and a washer. The AC has been running for days due to extreme temperatures, so the house is basically sealed. The plumber is suggesting a "smoke" test, i.e., toss a couple smoke bombs into the stack and walk around the house to see where the smoke leaks through wall the most. Does this make sense to locate source of sewer gases? - Lillian 7/6/12
Reply: smoke alone may not be adequate to find plumbing vent leaks as there is no pressure;
Lillian, I agree with finding the sewer gas leak but the smoke approach is inadequate or incomplete - it won't find a leak inside a wall or ceiling, for example and it can leave debris that clocks a vent line. Don't count on smoke leaking through the wall. Or if you try this quick and dirty method be prepared to have to look more carefully. I'd spend some effort homing in on where smell is strongest. If necessary to confirm it's the vent system a pressure test could be helpful. Check for the obvious - a loose or leaky toilet seal, a blocked or slow drain, dry plumbing traps etc.
Question: loud vibration noise in plumbing vent piping when toilet flushes
After flushing basement toilet there is a loud vibration from the vent stack piping. This has been getting worse and at times sounds like a ship horn. The two other toilets upstairs do not have this problem. We have been in the house for ten years and the problem just started in last few months. Our home is on a septic system but ground gradually drops away ( walk out basement ) so a septic pump was not needed for the basement toilet. There is only one roof vent stack, could there be a partial blockage in the line leading up from the basement toilet? - Frank 7/18/12
Frank I am not sure; I'd start by looking for loose plumbing vent piping.
Question: sewer odor seems to come from vents, not the drains
I have a strong sewer smell in my apartment. i cannot detect the smell when sniffing around the fixtures It is the same smell coming from the vents protruding from the apartment. If I leave the door open I can smell it I the hallway of the building. I have flooded water down drains for 10 days. - Jackie 8/20/12
Jackie it sounds as if you need a plumber to check the plumbing vent system for leaks or improper installation
Question: smell from plumbing vent encountered when outdoors
The odur problem I am encountering is outdoors and is caused by the vent pipe. If I am outside, and my husband drains his bathwater, an instant odor comes from the pipe on the roof.
Gail, depending on plumbing vent location above the roof and wind direction and site characteristics, a down draft can on occasion send plumbing vent stack odors down to a yard below. I'd try raising the height of the stack pipe above the roof, or perhaps installing a rotating wind-operated top cap on the vent that does not close the vent off but shelters it from the wind source.
Question: Sin, Tub, & Toilet Drains have terrible sewer smell - will pouring water into drains fix this?
We rent a home and it has the terrible sewer smell above the sink, bath tub and toilet in the main floor bathroom. There are no vents that we can find anywhere. What is there regulations , codes, or laws regarding this? We have told our landlord many times and they keep sending plumbers with our request but all of them but one would tell us to pour 5 gallons of water down the drains when we smell it. The last plumber said that it was not vented and they would have to vent it. That was 3 weeks ago. I have called the land lord and no word back. - Kathy Tucker 9/15/12
Question: strong gas odor comes from toilet when windows are open
We have a strong gas odor coming from our master bath toilet when windows are open in the master bath allowing a cross breeze. The vents are on top of the roof nowhere near windows. The gas is not present with the windows closed. We've replaced the toilet and had 3 different plumbers Reseal the toilet. We still get the gas when windows are open. Any ideas? - Jay 9/11/12
Jay, depending on plumbing vent location above the roof, window location and distance below the roof, and wind direction, site characteristics may be giving you a down draft that sends plumbing vent stack odors down into a nearby window. I'd try raising the height of the stack pipe above the roof, or perhaps installing a rotating wind-operated top cap on the vent that does not close the vent off but shelters it from the wind source.
Question: shower drain gurgles and stinks after flushing the toilet - is this an expensive repair?
We purchased a home about 10 months ago. The master bath shower had a previous leak and we hadn't used it since moving in. A few weeks ago we noticed after flushing the toilet in that bathroom a gurgling sound in the shower along with a stink odor. What is probably the cause and is this a big cost to fix. We are in the process to start working to figure out the shower leak problem. - Zina 9/08/12
Question: is it ever ok for a plumbing vent to terminate in an attic?
I inspected a 4 year old home recently. I found what I think were ABS plumbing vents terminated in the attic. I thought they might be for air admittance but they had no valve on them. Is it appropriate to terminate a plumbing vent in the attic? My gut and head both tell me "NO".
Dennis, I agree completely with your gut and head, as do the model building codes. Plumbing vents need to be terminated outside the building, usually above the roof line, though there are a few other possibilities - all outdoors.
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