Stinky Laundry Room? Stinky Bathroom? Check Your Traps.

Home Inspector with Structure Tech Home Inspections

Have you noticed any foul odors in your basement that you just can't get to the bottom of?  It might be sewer gases coming in to your home.  Every plumbing fixture needs to be equipped with a trap, which is basically a dip in a pipe that water fills up.  This water sitting in the trap is what prevents sewer gases from coming in to your home.  The photo below shows a "P-trap" - this is the type of trap you'll find below sinks, showers, and bath tubs.

P-trap explained

Toilets have their own built in traps, and so do floor drains.  The trap on a floor drain is located below the surface of the floor - the photo below shows a floor drain as seen from the side.

Floor Drain

The problem that home inspectors often find in basements is that floor drains or other plumbing fixtures in the basement never have any water flowing to them, so the water in the trap eventually dries out and allows stinky, hazardous sewer gas to come in to the home.  Because of this, abandoned or shut off plumbing fixtures are always listed as a hazard or required repair on Truth-In-Sale of Housing evaluation reports in Minneapolis, Saint Paul, and the rest of the surrounding cities.

P-trap with no water

Floor drains are the most frequent offenders.  If a floor drain doesn't have water flowing to it on a regular basis, the water in the trap will dry out.  A few common things that regularly drain to floor drains and help prevent the traps from drying out are AC condensate drain lines, high efficiency furnace condensate drain lines, humidifier drain lines, dehumidifier drain lines, HRV drain lines, and water softener discharge lines.  If you don't have anything draining to your floor drain on a regular basic, the water in the trap may evaporate.

rv antifreeze

One fix is to pour some RV antifreeze in to the drain.  RV antifreeze is cheap, sold everywhere, safe for the environment, and it won't evaporate.  It's made just for this kind of thing.  Another option is to periodically pour some water down the drain; you'll obviously need to do this on a regular basis, but it's free and easy to do.
Basement toilets are another frequent offender.  These are typically found in old Minneapolis and Saint Paul homes, and it consists of a toilet sitting out in the middle of the basement, with no privacy offered.  These toilets don't get much use, and the water in the bowl eventually dries out.

If you have an abandoned toilet in your basement, have it removed and have the opening to the sewer capped off.

Abandoned standpipes can be another source of sewer gases.  A standpipe is a stand-alone trap that typically receives the discharge water from a washing machine.  If the washing machine gets moved and is not longer discharging to the standpipe, the water will eventually evaporate.

Standpipe diagram

The fix for an abandoned standpipe is to cap it off or remove it.

Infrequently used bathrooms are the final common offender.  In larger homes with guest bathrooms that never get used, the water in the sink, toilet, or tub / shower can evaporate.

As with floor drains, the fix is to pour some RV antifreeze in to the fixtures, or remember to run some water through them every few months.  Easy.

Comments (32)

Chris and Dick Dovorany
Homes for Sale in Naples, Bonita Springs and Estero, Florida - Naples, FL
Broker/Associate at Premiere Plus Realty

I have actually run into this in my own house years ago with a downstairs bathroom that was rarely used.  I learned long ago that every few weeks to pour a bucket of water down the drain.  Problem solved.

Aug 22, 2012 12:05 AM
Vanessa Saunders
Global Property Systems Real Estate - White Plains, NY
Real Estate | Done Differently

Great post and an important tip. One could search a stinky house for odor source for hours and never realize where it's coming from!

Aug 22, 2012 12:22 AM
Ashley Connolly
Northeast Water Wells Inc - Jaffrey, NH

great post and tips if all else fails check the water quality :)

Aug 22, 2012 12:30 AM
Ann Samuelson
Suntree Inc. - Astoria, OR
Great point, I used to own a mechanical plumbing company, another liqquid that is usually on hand that works well on a dry floor drain, is cooking oil, it does not evaporate like water will.
Aug 22, 2012 12:31 AM
Margaret Goss
@Properties - Winnetka, IL
Chicago's North Shore & Winnetka Real Estate

You wrote this at the perfect time for me.  We have been dealing with this issue - but it's in our master shower which is used twice a day.  My husband has tried everything . . . except for the antifreeze which I will buy today.   Hope it works! 

Aug 22, 2012 01:02 AM
Charles Buell
Charles Buell Inspections Inc. - Seattle, WA
Seattle Home Inspector

Reuben, I had a seller meet us at the door one time and the first thing he said was to warn us about the "unexplained" odor in the basement that they had supposedly even had a plumber in to figure out to no avail.  It was simply the abandoned washing machine drain :)

Aug 22, 2012 02:42 AM
Andrew Mooers | 207.532.6573
Northern Maine Real Estate-Aroostook County Broker

Great advice. Unless you are showing properties where the agent, broker, and buyers all have serious head colds. And are breathing through their mouths.

Aug 22, 2012 04:12 AM
Sandy Acevedo
951-290-8588 - Chino Hills, CA
RE/MAX Masters, Inland Empire Homes for Sale

It's a stinky job, but somebody has to do it.  Better that than clients rushing out of the home.  Didn't know that about the anti freeze....

Aug 22, 2012 06:25 AM
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

Love it!  Drains can dry?  Gee, who knew!  Those little brown guys look mean!

You forgot to mention duct tape.  That could solve the problem too!

Aug 22, 2012 07:17 AM
Donald Hester
NCW Home Inspections, LLC - Wenatchee, WA
NCW Home Inspections, LLC

Reuben, Great post. Trap primers are also an answer but a litlle more costly.


Aug 22, 2012 08:59 AM
Myrl Jeffcoat
Sacramento, CA
Greater Sacramento Realtor - Retired

Very interesting.  I think many homeowners think things go down and that's the end of it. . .until they don't:-)  You offer great tips and solutions for a stinky problem.

Aug 22, 2012 09:10 AM
Evelyn Kennedy
Alain Pinel Realtors - Alameda, CA
Alameda, Real Estate, Alameda, CA


I have learned so much from the property inspectors on ActiveRain.  I have the answer to my question, why is that basement drain so smelly.  Now I know what to do with it.

Aug 22, 2012 09:11 AM
Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Delivering the Unbiased Truth.

Sally and David - on vacant houses, absolutely.

Dorie - I just found that at an inspection on monday; big house, recently remodeled, no trap installed at the new bathroom sink!

Chris - you got it :).  Just run a little water.

Debbie - that's right.  Those basement toilets never get much use.  

Ginny - such an easy fix.

Aug 22, 2012 11:11 AM
Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Delivering the Unbiased Truth.

Scott S - Ok, you got a belly laugh out of me with that comment!

Joy - if you look in the toilets and you see pink stuff, you know it's already been taken care of.

Beth - next stop: Home Depot for some RV Antifreeze.

Michael - thanks.

Harry - hopefully that's what you're smelling :).  If that ain't it, it might be a tougher solution.


Aug 22, 2012 11:13 AM
Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Delivering the Unbiased Truth.

Richie - as always, thanks.  Much appreciated.

Chris and Dick - grab some antifreeze and it will no longer be a regular maintenance thing.

Vanessa - I've talked to so many homeowners that have lived with these odors and never figured them out.  It's always an "aha" moment for them when I explain the odor.

Ashley - You're right, I've smelled some pretty nasty smelling well water before.

Ann - I never thought of cooking oil.  Thanks for the tip!

Aug 22, 2012 11:16 AM
Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Delivering the Unbiased Truth.

Margaret - if you use the shower twice a day, antifreeze isn't going to help.  Try looking down the drain with a flashlight; can you see water in there?  If not, you might not have a trap.  If that's the case, you'll be looking at a more extensive (and expensive) repair.

Charles - I think it must have been time for that plumber to retire ;)

Andrew - no thanks :)

Sandy - If you ever find pink stuff in the toilets at bank owned properties... you'll remember this.

Jay -  well, yeah... but that just goes without saying, right?  I mean, duct tape will fix anything :)

Aug 22, 2012 11:20 AM
Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Delivering the Unbiased Truth.

Donald - I'm familiar with those trap primers, but I've never actually seen one in the wild.  Have you?

Erica - me too!

Myrl - thanks.

Evelyn - glad to help, thanks!

Aug 22, 2012 11:22 AM
Bill Reddington
Re/max By The Sea - Destin, FL
Destin Florida Real Estate

Common sense says make sure there is water in the toilet or drain. Same situation if a disposal hasn't been run in a while.

Aug 22, 2012 02:10 PM
James Quarello
JRV Home Inspection Services, LLC - Wallingford, CT
Connecticut Home Inspector

Like Don said, a trap primer. I have recommend them, but haven't seen one "in the wild". 

Aug 22, 2012 09:21 PM
William Feela
Realtor, Whispering Pines Realty 651-674-5999 No.

This is one of the things I also tell my clients.  If it has not been used as of late, dump some water in it. The Anti-freeze is a great idea.

Aug 25, 2012 05:04 AM