Fixing Mobile Home Venting Issues and Sewer Smells

mobile home plumbing questions and answers featured image

Today’s article is the first of a new series we’re starting called Ask a Mobile Home Expert. We’ll be covering fixing mobile home venting issues and sewer smells that can occur when your ventilation system isn’t working properly.

Since I began Mobile Home Living in 2011, we have published over 500 articles and received over 6,000 mobile home-related questions and comments. I’m proud to say that I have personally replied to every single question! In several cases, I was able to get an expert to answer the questions (being married to a licensed master plumber/contractor has its perks). That’s how we got the idea for this new Ask a Mobile Home Expert Series.


plumbing ventilation system diagram - Ask an Expert about Mobile Home Venting Issues
A basic portrayal of a ventilation system. Source: Pinterest


Fixing Mobile Home Venting Issues and Sewer Smells

Your mobile home plumbing’s venting system is more important than most of us realize. Every plumbing system has 3 parts: the supply line where the water comes from, the drain lines where the waste goes, and the ventilation lines that allow the system to breathe and pushes the sewer smells up and away from the home.

Mobile home venting systems are pretty cool! The way it all works together to create a happy and healthy home is neat. Imagine if we had to live with our sewage smells – what an awful thought! Here are a few scenarios of homeowners fixing mobile home venting issues.


Fixing Mobile Home Venting Issues Caused by Washing Machines

We are having a sewage odor problem that comes and goes. It’s worse in the laundry room and since the air conditioner unit is close the smell gets distributed all over the house. We have a brand new septic system (only 1-year-old) and only the kitchen and the toilets drain to the septic system. Everything else drains to the backyard as gray water. There is no odor where the gray water drains, and there is no odor under the house. A plumber fixed the ventilation stack about 9 months ago and within about 2 weeks we had no more odor problems until about 3 weeks ago. Since then, the plumber has come back out, but we are still getting the smell. Any ideas?

We have a brand new septic system (only 1-year-old) and only the kitchen and the toilets drain to the septic system. Everything else drains to the backyard as gray water. There is no odor where the gray water drains, and there is no odor under the house. A plumber fixed the ventilation stack about 9 months ago and within about 2 weeks we had no more odor problems until about 3 weeks ago. Since then, the plumber has come back out, but we are still getting the smell. Any ideas?

There is no odor where the gray water drains, and there is no odor under the house. A plumber fixed the ventilation stack about 9 months ago and within about 2 weeks we had no more odor problems until about 3 weeks ago. Since then, the plumber has come back out, but we are still getting the smell. Any ideas?


It sounds like the water in your p-trap is getting siphoned out of washer drain. If that isn’t the culprit, check to see if the AC unit drain is tied into the sewer. If it is it will need to be disconnected as it doesn’t have a p-trap and will allow the odor to escape.


washing machine p-trap diagram - mobile home venting issues and sewer smells - Ask a Mobile Home Expert Series

Sometimes, negative pressure can siphon the water 
out and allow sewage smells to come into the house.

Image source.



Common question about fixing mobile home venting issues: Can Mobile Home Ventilation Lines Have Elbows?

We have a sewer smell in our bathroom and bedroom. I checked ventilation pipe that extends through the roof. Can a ventilation pipe have an L-shaped pipe? I put a wire down pipe and hit something hard about 12 to 18 inches down.

Yes, your vent stack will usually include elbows. A vent elbow can be a complete 90 degrees whereas your water line elbows have a curve instead of a corner.

If you have a stoppage you’ll definitely want to get that cleared, that’s probably your problem. The system has to be able to breathe. You could try pouring water down the vent to see if it’s a clog. If it’s an elbow it will drain, if it’s a clog it will backflow.

 mobile home venting issues and sewer smells - Ask a Mobile Home Expert Series - elbow shown in vent line

 This diagram shows a 90-degree elbow in the vent line.

Washer Drains into Bathtub in Mobile Home 

We invested in a 2004 Fortune double wide home, it has two bathrooms, a master, and the guest. The other day I took a shower and we did the dishes and everything was fine,  with great drainage. However, my fiance did a load of laundry and when it when into its spin/drain cycle all that water started coming up into both tubs!

It left about 2-3 inches of water in them and you could tell it was dirty laundry water, they didn’t drain at all for almost 10 hours. Also, the water in the toilets is gone, I took the lid off of the toilet and let some water into the toilet bowl and as that water went into the toilet bowl you could see the water rising inside the tub.

Yet, the kitchen sink doesn’t seem to be affected or to affect anything at all. I have searched and searched for answers. Help!

It sounds like you have a stoppage. As a result, this would make the drains slow since you aren’t getting the pressure equalized in your traps so it’s pulling into your toilets.

You probably happened to use just enough water to fill the trunk line up until it came out of tub drains. The water gets sucked out of the toilets because the trunk is full of water so it cuts off the toilet’s ventilation which siphons out the toilet.

You’ll need to find where the clog is and snake it out. You can try a residential snake available at Amazon here (affiliate link) but sometimes it takes an industrial snake that shoots high-pressure water so you’ll need to hire a plumber.

Snaking a Kitchen Sink with Grease? 

If you have grease in your kitchen sink a snake will not be able to unclog it in most cases. Imagine a bowl of pudding, you can easily stick a spoon in it but when you pull the spoon out the pudding just goes back where it was. That’s what the grease does with the snake. It will go right through the grease.

Also, don’t pour grease down your kitchen sink. It will cause issues eventually.

Mobile Home Venting Issues cause Slow Drains

I am renting a manufactured home that has several previous renters. I started experiencing very slow draining & backing up in my kitchen sink. I’ve tried Draino, snaking & plunging it, taking the pipes apart & cleaning them; nothing worked.

I loosened the air admittance valve cap & the water drained perfectly. I cleaned the vent stack thinking that may help. As soon as I tightened the valve cap back up the sink stopped up again. Finally, I loosened the cap again & the sink is draining just fine. Could I need a new air admittance valve cap?

Yep! An auto vent is a continuously working mechanism that opens and closes on demand. It sounds like it is just worn out. This is a very common mobile home venting issue.

They are around $25 at your local home improvement store or order one from Amazon here (affiliate link).

Have More Questions about Mobile Home Venting Issues or Smells?

These questions are good representations of average mobile home venting issues and sewer smells that can occur in the typical home, but there’s a lot more to it all.

As always, thanks for reading Mobile Home Living!

Disclosure: Any answers to questions posed about fixing mobile home venting issues and any recommendations or information provided herein should not be used as a substitute of an expert or any relevant professional that has inspected the issues in person. 

18 thoughts on “Fixing Mobile Home Venting Issues and Sewer Smells”

  1. How do I plumb up the sewer line under the house how do I put it together I just got a brand new double wide I need to know how to plumb up the sewer and what line under the house or for the water so they got two in the middle of the house one is white and one gray

    1. Hi Jason,

      Congratulations on the new home! You’re gonna need to hire a plumber. This is not the kind of job an unlicensed person should be doing. You have to know proper grade for one and for two a plumbing system is an extremely complex system that includes 3 different subsystems that must work together. The dealer you bought the home from should be able to help you (and usually installation and setup are added to the loan). Best of luck!

  2. About a year ago, we started getting sewer smell in our home. Especially when using the washing machine. We had the septic tank pumped out last year, which was not full at the time so that wasn’t the problem…and the smell remained. Tried changing out the caps on the vent pipes. This helped a lot. But the smell has recently come back with a vengeance! The horrid smell comes up through the furnace and floor vents now. We do not use the furnace, so we covered all the floor vents. This has helped but not completely. And at the furnace it is nauseating! I had someone spread lime underneath the mobile home but that only took the smell away for that day.
    When my son and husband crawled under the home, they said it did not smell like sewer nor could they find any leaking pipes. suggestions??

    1. Hi Mallissa,

      You may need to make sure your sewer lines aren’t open under the home first. If it’s not that, make sure your septic tank or waste line is not full or backflowing. If it’s not that, you’ll want to check the vent system and make sure there is no cuts or separations.

      It’s def fixable, it’s just going to take some sleuthing to see which issue is causing it. It’s probably going to be one of the 3 I mentioned. Best of luck!

  3. Hi. I am renting an older mobile home and it has major problems. If the vent cap on the outside of my home is tight ALL my water a sewage fills up in the bathtub. It was snaked and there was no obstruction. If I leave the cap loose everything drains out of the pipe into my yard. I don’t know what to do. It started with the washing machine draining and all that water filled up the bathtub..Thank you for any help you can give me.

    1. Hi Linda,

      If I’m understanding you correctly, your vent stacks should not be capped at all. It has to allow the gases to escape and to keep the system in balance and ‘breathe’ so it has to be left open.

      Take the cap off and you’ll be fine. Rain will get in, as will birds, but you can put a screen over it to keep the birds out if you must (it’s fine without it though) – the rain is minimal and doesn’t hurt anything at all.

      The washing machine was probably vented to go out into your yard. It’s not legal in most places but many people do it to keep the sewer from filling up. It’s common out in the country or on shared septic systems.

  4. Hi. Every time I use the kitchen sink I have to go back to the bathroom and flush the toile. If I don’t we won’t get rid of the nasty rotten eggs smell that starts to fill up the mobile home. My ventilation/ pipes are along the inside, against the wall. From the kitchen through the living room and my son’s bedroom to the bathroom. Any thoughts why I can’t just start washing dishes without getting that awful smell?

    1. Hi Victoria,

      It definitely sounds like something is sucking your traps dry. There’s a partial clog holding water in the trunk line or an auto vent may be going bad. Either way, your system is off. First, look for an auto vent and replace it. Then start snaking.

      Best of luck!

  5. hello,
    thank you for this great newsletter and ask an expert, cause where i live, no one has heard of a “stink pipe” or “vent” or “stack”, etc. i am well past my irritated stage with this problem. i have read your article on sewer smells. being a female with a husband who doesn’t know much, i’m left alone to to investigate the problem and, well, like i said, i’m very irritated right now.
    my issue is – every time i do dishes, the sewer smells come to the kitchen, living room and well, all over. i’ve put zeps heat down and allowed to soak over night in all drains, poured hot water the next morning, but nothing happened. where could this clog be? i can’t see a pipe on my roof unless i get up on ladder and it’s like “heck” trying to get anyone to come out who knows mobile homes! (Screams). if the pipe on roof is clogged, how do i unclog it? if it’s not the pipe, where do i begin in the house? also, how do i put an auto vent in bathroom or kitchen? is that simple? i look forward to your reply. thank you for allowing me to vent – ha, pardon the pun!

    1. Hi Laura,

      I would try installing an auto vent on your kitchen sink first. If that doesn’t work then start snaking out the vent stack and the waste lines. Most of the time it’s a grease issue at kitchen sinks though. Best of luck!

  6. I purchased a brand new mobile home about 2 months in I started getting a wet dirt smell every time I walked into my home as the days went by it started getting stronger and stronger I then noticed my air conditioning coil was freezing up and defrosting causing a water spill on my carpet. The water dried up and the air company placed a brand new coil, but that smell is still so strong in my home, but the carpet itself doesn’t smell. The smell is on my clean clothes that hang in my closet, the smell is in my hair my furniture. As soon as anyone walks into my home they ask what that smell is. Its so bad my car even smells I guess our clothes and hair rubbed off on the seats or something but it truly is humiliating. I was at the bank and opened my purse and out came the disgusting odor of my home. Does anyone have an idea of what this might be. Ive never lived in a manufactured mobile home so I don’t know what it could be.

    1. Hi Nani,
      I’m not sure what that could be other than mildew or mold that is growing under your carpet. I’d lift it from a corner and see if you can see anything either on the carpet pad or rotted wood on the subfloor. I’m still doubtful that it could be that strong to follow you. Maybe look under the home for a dead animal?
      This probably wouldn’t be a manufactured home issue, just a home in general kind of issue since manufactured homes use similar materials as a site-built home (even if the material is cheaper).

      I’d definitely have someone check out under the home, vents, and under the carpet. Best of luck! Let me know how it goes!

  7. Drainage problem with the washing machine and kitchen sink. The drain pie was cut and drains on the dirt on the side of the mobile home by the kitchen. It’s flooded all the time. It gets under the house too. The rain makes it worse. I saw a 3″ x50′ corregated drain pipe at Lowe’s for $29. Can I attach that to extend it out into the property to drain out there to move the water away from the house? Do you have any other suggestions? What are the possible damages this may have caused already? The place looks bad and is falling apart. Thank you.

    1. Absolutely! A true ditch with a metal grate is also a good idea. This will keep cars from crushing it too. We have a couple across our driveway for rain diversion – all we do is clean the culvert/ditch out every couple of months.

      Best of luck!

  8. I bought a 95 manufactured home double wide. It has what I call a “fresh air fan” in the family room ceiling that is operated by a switch on the wall. When I bought the home the fan assembly and motor was missing and I cannot find a replacement anywhere. The fan vents straight up thru a roof vent. I would like to find a replacement motor and fan assembly or a similar size top venting fan so I do not have to replace drywall. Do you know where I could find a replacement, I can only seem to find bathroom fans. I have had these in my homes before so I know there are commonly installed. Just not commonly found to replace.

  9. Hi, we just bought one of those great craigslist mobile home finds. We are going to be remodeling throughout. It has an island range with a range hood over it, and I’d love to customize it to a farmhouse look. Is it possible to hang a heavier hood cover in a mobile home? I’d hate to pull the roof down on us. Right now it is basic generic straight hood cover. I would love to do something like this.


    1. Hi Charlote,

      A nice hood really does make a kitchen stand out! Great idea! You shouldn’t have any problems as long as the hood isn’t too heavy – just make sure it is secured into studs. I’ve seen a homeowner build their own hood cover just like that with mdf (or maybe it was thin pine board) and trim.

      Best of luck!

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