Plumbing Vent leaks (C) Daniel Friedman Cheryl LidawerPlumbing Vent & Drain Noise & Smell FAQs
Q&A on Drain Noises, Gas Smells & Septic Odors Set#2

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More plumbing vent piping & system FAQs:

Often noisy or slow building drains or drain odors are traced to problems with the building's plumbing vent system piping and connections. These FAQs help diagnose and specify the repairs for those annoying problems.

This article series describes 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. Causes of gurgling noises at drains, and why some fixtures "gurgle" when a toilet is flushed nearby.

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Plumbing Vent Piping Defects May Cause Drain Noises or May Release Dangerous Sewer Gas Odors Indoors

Pumbing vent damaged by sliding snow (C) Daniel FriedmanThese questions & answers about diagnosing and fixing smells, noises, leaks traced to the plumbing vent system were posted originally at PLUMBING VENT DEFECTS & NOISES - home - be sure to see those diagnostics. Or some Q&A may also have been posted as comments at the end of this very page.

On 2017-08-25 by (mod) - approaches that can help sort out this toilet odor problem


There are a couple of approaches that can help sort out this toilet odor problem.

One is to spend time in fresh air so that your sense of smell will be at its best, then enter the bathroom and sniff around the toilet base, sink trap, tub trap, etc to see if you can spot where odors are strongest.

Two is to flush the toilet and listen for clues that there is a venting problem like blocked or leaky or inadequate drain line venting. If on toilet flush a nearby sink gurgles then venting is not working.

Three, more involved is to have the drain system pressure-tested by a plumber who knows how to do that. The fact that smoke came out of a vent is not the same as a pressure test. Smoke shows that air passes up and out of the vents but doesn't tell us
if the vent is also seeping sewer gases into the building from leaks where the vent passes through the structure. So the technician's comments are incomplete.

at SEWAGE ODOR SOURCE LOCATION I list a series of other causes of sewer gas smells that you should look-through. That article is part of a series of procedures on tracking down sewer gas smells.

Do keep me posted as what you learn will help others. - Mod

On 2017-08-25 by Sue - smoke test didn't find source of toilet odors in the vent system

Plumbing question I think--New construction home with unfinished full basement with odd smell appears to emanate from two toilets both on first floor. No smell in second floor bath nor laundry or kitchen. Had both toilets reset with new wax rings. No change.

Builder agreed to change out the toilets with identical but new ones replaced wax seals again. Flanges are level with floor. No change, odor still existed. Another plumber came and reinstalled toilets with new wax seals.

Master bath toilet on tile he caulked with 3 inch opening in back and smell is now lessened but still slightly noticeable. Powder room toilet smells just as awful as ever. Dropped bleach into toilet bowl, saran wrapped bowl, smell still there.

Had a smoke test done. No smoke in home or attic spaces(there are two). Have 5 vent stacks--kitchen, master bath had plenty of smoke coming out, roughed in basement toilet stack had nothing as expected, remaining two only one vent had smoke passing through to outside.

I am assuming one vent is for second floor bath, one for first floor powder room and laundry.

Technician stated since no smoke in house, even though no smoke exiting vent indicates no problem. It is possible the vent stack is non-utilized but since all other rooms appear to have their own vent I find it unusual that all three remaining rooms--powder, laundry and second-floor would be vented together. There is no gurgling noises when multiple systems are used.

Could there still be a vent problem, specifically the vent that was smokeless?

On 2017-07-14 by (mod) - Check air return opening to see if there is a sewer gas leak or a dry drain trap nearby

Wayne, Speculating,

Check each of the air return openings first to see if there is a sewer gas leak or a dry drain trap nearby, such as a basement floor drain near an air inlet on an air handler.

On 2017-07-14 by Wayne H.

If I flush a toilet or run the shower while my central air is running, I often (not every time) get a foul sewer smell throughout my home's duct work. I'm on public sewer. This has been going on for years.

On 2017-07-14 by (mod) - tree roots block drain line?

Thanks for the follow-up Jim R - that will assist other readers. Keep us posted. Let me know in particular what other sort of blockages are in the in-ground drains or piping; for example tree roots

On 2017-06-15 17:48:23.419788 by Jim R

Okay, the plumbing is up and running again and it appears the situation will be resolved for somewhere between $2-2,500. The drain people came out but felt the septic tank was likely the issues so they left. Septic tank was working fine but since it was open and not cleaned in 37 years, as far as I know, had it cleaned out.

The drain people followed up and water jetted and scoped the pipe. There was an accumulation where the drain pipe was damaged so they'll be sending someone out to deal with that next week.

Thanks for the response, I got to that diagnosis on my own after I posted. I went up on the roof and snaked the vent in case some critter or tree droppings had clogged the 3" vent and hit nothing that indicated any blockage.

I have a pro coming out in the next half hour and will post the ultimate resolution for anyone experiencing symptoms similar to mine. The ugly part is that I have no diagram of what the system looks like other than knowing it's a sand mound system that's 37 years old. The township was very rural back when it was built and they have no documentation to help me.

On 2017-06-13 by (mod) - main waste or septic problem shows up as bad drainage


Your description makes me think the problem is in the main waste line or is a septic problem. We should be able to verify that by noting that running water anywhere in the building produces the sound.

Conversely if the sound occurs only when water is run in a specific location (kitchen) we'd guess that the blockage or vent problem is between that set of fixtrures and the rest of the drain system.

If it were my home I'd go ahead and have a plumber snake the line as a step that might repair a clog and that is also diagnostic - what sort of blockage is encountered? where was it in the piping system? If the snake goes freely to the tank we know that the next step, inspecting the septic tank, is likely to show us that the tank levels are abnormally high and the system is backing up.

On 2017-06-13 by Jim R gurgling in the hall bath at the back of the house

I have an issue that developed very recently. I was running the dishwasher in the front of the house and was in the bathroom and I heard gurgling in the hall bath at the back of the house. The drains run from the back to the front.

There is a large (maybe 3") vent through the roof in the back that services the two bathrooms and the washing machine plumbing and a second vent that runs up near the kitchen for venting that area. Last year I had an issue with the kitchen not draining and after some trouble shooting, I found that the vent near the kitchen was blocked with something. Snaking the vent pushed whatever was in there.

So yesterday my gf heard the same gurgling when she ran water in the bathroom sink. I had been working in the garage and had some things to move to the basement. When I got down there, the floor around the hall toilet drain was flooded and I could see water coming out from the area of the drain and getting on everything. I realized I had run a load of wash to clean some garage rags earlier.

I put a galvanized container beneath the pipe a few minutes ago to catch most of the water if it ran out and put a load of dishes in the dishwasher to see if that would run out or drain normally. Well, the water backed up to the toilet in the back of the house.

Would a clog in that rear vent create a backup from water down the line to the kitchen or, as I fear, am I dealing with an issue with the main out to the septic system?

On 2017-05-23 by (mod) - how to stop wind problems and downdrafts at plumbing vents

I'd look for a vent top wind screen or cap - there are models that look like a 90 and that rotate to face the elbow's back into the wind. If you can't find one let me know and I'll dig up some product examples.

On 2017-05-22 by - sloshing in toilets

I live in a very windy part of the country. When the wind howls we get extreme sloshing in the toilet and a sewer smell in some of the sinks.

The roof vent is up to code. It would seem that we are
getting a back draft. When the days are calm there is no problem. I have seen P-traps or 90's added to the vent. Would this help?

On 2016-12-18 by (mod) - low water in the toilet bowl


Your home could have a vent clogging from frost but low water in the toilet bowl suggests that the flush or fill valve needs adjustment

Use the search box just above to search for GURGLING DRAIN NOUSES to see diagnosis and repair information

On 2016-12-13 by Carolina

We just recently began seeing a very low water level in the toilet that fluctuate with the heavy winds. We also notice gurgling in the bathroom sink. We've lived in our home over ten years and this is happening just in the last month. Could it be clogged vent stacks and if so, how are they checked and cleared?

by the way, thank you so much for this web page. My husband is a disabled vet and we don't have the money for plumbers. He's pretty good at this sort of thing but this one has him wondering. Thanks again! (also there is no odor)

On 2016-07-31 by (mod) - wind carries sewage odors

Andrew McGibbon said:
In the event where you are smelling the odor coming from vent stacks outside the house, as explained above, this can be the result of wind vortexes that carry the smell down and around the house. This can be caused when a house is situated against a hill or line of trees.

The wind carries the odor down from the septic vent on your roof or yard vent instead of carrying it away. One solution, as indicated above, is to raise the height of the pipe. Another is a septic vent filter.

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


I'd try a simple sniff test to see if you can track down the strongest odor source. It's not a big job to pull a toilet and replace a doubtful wax ring if that seems to be the trouble area.

Sometimes drains smell even if not blocked, and even if the vent system is working - due to accumulation of hair, sludge, and bacteria in the drain trap. You might try cleaning that smelly shower drain.

It's worth considering with care your observation about the near-location of all of the smell-suspect fixtures. See if you can determine that all of them share the same drain or vent pipe.

Finally, your plumber's suspicion is worth considering, but you might be able to sort that theory out by taking note of the history of the smell problem. If the problems are long-standing and relate to weather/wind, a vent problem could be more suspect.

Question: long horizontal plumbing vent runs can leak into ceilings below

One potential issue that was not mentioned in the article:
I have a horizontal vent run of ABS in my attic, approximately 20 feet long. I'm assuming multiple vent stacks are being joined. I recently had a water leak from the horizontal pipe section onto the 2nd floor ceiling. Upon inspection I found that the horizontal run had a split along the side of the pipe. It appears that rain water had been collecting in the horizontal section and must have frozen, splitting the pipe.

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.


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