2 to 4 cups of water at a time is plenty. If you see water in the toilet you have a seal. Add the water on a weekly basis and flush the toilet once. In the winter it doesn't take too long to evaporate enough water to break a seal.

Thank you, it may be just that. I didn't think about how dry the house is in the winter. One thing that bothers me though is that I thought that if it were just an open trap that the smell would go away entirely pretty quickly - within hours if the window were open a little. But there is a fainter version of it lingering. Most of it did go away. Is there any way it can get behind the walls or anything like that?

There are always other ways with plumbing....but it sounds like you just need to pour a cup of water in those traps every month or so.

I wonder if any of this has to do with the fact (I think) that our bathroom fans just vent into the attic not outside.

There is still a lingering but somewhat fainter oder of sewer gas in the bedroom and bath. I guess I should get up in that crawl space. WHat am I looking for?

If your fans exhaust into the attic and you use them on a daily basis, I would be looking for mold, wet insulation and wet boards. That would be a lot of moisture to throw in a confined space. Run the exhausts to the outside, either roof or eave vent.

This problem has come up more than once on this site. When there is water in all of the traps and there are no sewer pipes cracked or open, then it's pretty hard for sewer gas to get into your house. If it smells like sewer and not just a musty smell then.... as I remember, almost every time someone has written about the problem it hasn't been sewer gas they are smelling, but a dead rodent or such somewhere in the house.
If you can go back and find it in this site, someone had almost the exact problem you are having. The odor would come and go. They found a dead mouse or squirrel in the ceiling.

Thank you about the rodent. Originally I thought that was what it was, a dead mouse in the wall. I figured after a while it just sort of dried up but then I thought how many times could that happen? Well I suppose they could live in the attic.... I will say, it does seem like the smell is always in the same vicinity but not exactly the same place. I will look for those posts. I will search for ???

dead rodent smell ?

Well DH crawled up in the attic over to the fan area, nada. There is evidence of mice but not there. I am now thinking one died in the wall and we need to cut out the decon.

Is it possible that the lingering smell might be from drapes, shower curtains, and towels absorbing some of the smell and the slowly release it back into the air after the trap is closed and the air cleared out?

Though your toilet may have water in the bowl, the wax seal could be dried out or compromised in some way. Especially if the toilet wobbles and is not secured completly to the floor. Gonna have to get down to on the floor with the nose for that one.

Checked the area near the base of the commode. I did not detect any smell there. It seems like it is generally eminating from the area of an exterior wall.

It gets getter and worse but has never been as bad as the first day or two. Dead mouse in the wall? Does that happen over and over a couple times a year? Because that is what is happening here.

No drapes or other cloth in the bathroom.

Crazy ~ as this sounds ~ I had a mouse or rat die in my wall - why do I know that it was a mouse or rat - I knew the smell.

I am curious does the sound come back when it rains outside or if it gets damp in the area ~ possibly refreshing the mouse or rat carcass. Just a though ~ it happened in my walls ~ finally disappeared.

If is an outside wall my first thought would be no plumbing in that wall - if there is a short drain vent outside you may be drawing in the smells from outside.

Two other questions are ~ are both P-traps tight the one under the sink for the sink and the one under the bath tub?

The only other possibilities would be a cracked ABS joint.

Either way ~ you still have some detective work to do.

Thanks. What is an ABS joint?

if you have found signs of mice in the attic, I would put my efforts toward finding out how they are getting in. Yes it could happen over and over, the smell coming and going. My sister's house, baby mice ended up on the pipe in the furnace, didn't smell too good. An exterminator told me the smell will last a couple days and disappear.

I would say the smell has lasted a week but it is almost gone now. It was powerful at first. We will look around for holes. I think they are coming in through the garage probably which is against this bathroom wall.

Myrtle, did you ever solve this problem? One other way to check for mice...... Sit quietly in the room late at night and listen for scratching sounds in the wall. If you hear them, you have mice (or something else). Sometimes I have had the dead mouse smell linger for ten days. Traps are better than decon. Peanut butter and cheese usually do the trick!

bump.

We had the same issue, this solved it quite well: Zep Drain Care® Buildup Remover. You can find it at your local big box hardware store. It will safely eat away the bacteria buildup in the pipes that are causing the odor. In addition to this, keep the trap filled with water too. We use it about every two months and the odor has not returned.

If your local plumbing code is based upon the IRC(Inernational Residential Code) it could be a problem with your DWV layout.

The IRC requires that all structures must have one "Main Vent" that must run undiminished in size from the house "Main Drain" through the roof. Once that is achieved when auxiliary vents are required, the may terminate through the roof, in the attic space or in some instances, through a side wall. The IRC also permits an unlimited use of AAV's (air admittance valves, commonly called cheater vents or studor vents).

While it may be code approved, terminating a vent in the attic space is never a good idea for two reasons:
1. the excess moisture discharged from the vent may collect in your insulation which would then greatly reduce the value of the insulation, not to mention that it creates a high risk of mold.
2. Many of the components in sewer gas are heavier than air, so if it is terminated in the attic space, the heavier than air gases will go downward and can permeate through your ceiling material causing the odor.

Very few homeowners, and sadly, even many professional insulation installers are not aware that there may be plumbing vents in the attic, and when installing insulation often those vents get covered, which then increases the chances of the sewer gases settling into the living space.