It does sound like it could be a venting problem. The water in the trap of each fixture serves as a blocker of fumes coming into the house. If the water is siphoned off then there is nothing to block the fumes. The toilet is easy...if you can see water in the bowl the way it should be, then there is little chance of odors getting by the water. So, it comes down to the tub/shower or lavatory. I think if you put your nose right down to each of these, if there is sewer gas coming up, it should be pretty easy to detect. Then it's a matter of finding why the water is getting siphoned out of the trap. The venting issue that you mentioned is a good place to start.
You didn't mention what was under the bathroom. Could a pipe be disconneced there? I mean the vent can get plugged up, but normally it's a 3" or 4' pipe and it takes something like an animal building a nest to cause that. I would definitely be checking for leaks first.....that only takes a few minutes without any climbing on roofs:-)

Well, it's a slab foundation so under the bathroom is just the foundation. I've checked under both bathroom sinks and there are no leaks. It's hard to pinpoint where the odor is coming from because it's so strong in the room that I can't tell if it's just the room I'm smelling or the drain. The shower drain does have some odor but it didn't seem strong enough to be causing the entire bath to smell (master bath is about 200 sq. feet.) I have two walk in closets off the bath and a seperate toilet closet and if those doors are all closed there are no odors in those rooms so it is definately coming from somewhere in the bath which probably means one of the jack and jill sinks, the bathtub, or the shower. I haven't gotten on the roof yet but I will this afternoon.

I'll be curious to know what you find.
Mark

OK, I went ahead and had someone come out. They don't do smoke tests but did use a "sniffer" and it was their opinion that the odor is coming from a vent pipe in one particular wall of our bathroom. I've scheduled a company that specializes in smoke tests to come and find out for sure exactly where the leak is coming from. The plumber tested all the drains and said he didn't think the odor was coming from any of the drains/faucets or under either of the cabinets. Investment so far: $49 I'll keep all posted as we find out more.

biggdan,

Just an idea mind you, but how about blocking up one drain at a time with a wet reg and see if you can isolate the smell that way.

best of luck with the hunt, rredogg

You may find that the problem is not a leak but rather a "Stupid provision in your plumbing code". While the Uniform Plumbing Code requires all vents to terminate through the roof, the International Residential Code requires all structures to have one "main vent" that runs undiminished in size from the main drain through the roof. After that, the code permits auxiliary vents to terminate through the roof, in the attic space or through the wall under certain restrictions.

Often we find that a vent was terminated in the attic space and later someone added additional insulation and unknowingly covers the vent opening. This causes the vent gases to expel under insulation and later permeate down through the ceiling into the living space.

If you find that you do have vents terminated in the attic space the best remedy would be to extend it up through the roof.

Maybe its a dead animal.

I had a friend with a store and a rotten smell. A plumber came and checked all of the plumbing and all was okay. Someone suggested a dead rat in the wall and turns out that's exactly what it was. It sure smelled like sewer gas to me.

Dead Rat next to Master Bathroom exhaust fan. Total Cost: $444. That was one freaking expensive Rat!

Follow up:

I was quite surprised when the plumber finally got above the master bathroom (took some effort because of the layout of our home) that he found a dead animal. We had considered this possibility but had dismissed it because of the coming and going nature of the odor. The odor was always worst in the morning and at night. The only theory I have is that in the afternoon when the attic heated up, as well as the interior of the home, the air tended to flow out of the home as well as the attic and then at night as the attic and home cooled the air from the attic space was more prone to flow/sink/push down through the exhaust fan. Anyway, the plumber reports that he heard more "squeek squeek" noises when he was in that area so I probably have more live rats/mice (not sure which it was because I didn't look at it) in the attic. I'll be trying to address that next so we don't have to go through this again.

Glad you found out what the problem was. I always thought rats preferred basements as opposed to attics but I guess they will go where ever. Normally if they are above, you can heard them moving around.

This is why I don't use rat poisen. They end up dying in the house and in the walls. Get some real big traps from Home Depot or Ace. Usually mice don't smell as bad as rats. I would ask your plumber if it was a mouse or a rat. You need to know in order to get rid of the rest. You should check out what your insulation looks like up there. Rodents leave droppings and urine in the insulation.

Good luck.

I had squirrels in my attic and kept trapping them but... I finally installed an electronic thingy that plugs into an extension cord and it gives off a 'beep' sound that mice, squirrels and rats can't tolerate. I run this thing 24/7 for the past 4 years. No more animal problems. The squirrels were nesting above the bathroom.

What is the name of your electronic thingy? I would be interested in one for squirrels.

On that electric thingy.....there are numerou brands and I'm not sure any one is better than another. They are commonly found in hardware stores or HD. I've used them successfully for squirels AND have driven bees/hornets out of an attic with the device. Don't ask me why it worked,but it did.

I have a similar problem. The odor occurs now when I flush the main bathroom toilet or run water in the master bathroom faucet, so its probably vent related. Would running a snake down the vent tube from the roof solve the problem?

I have a similar problem but in my garage..for years and i mean years..there's been a real foul odor coming from area where i have washer/dryer..behind that wall is a small half bath. I've had pest control, etc. in trying to see if it was dead animal..but they couldn't find anything..can anyone help me pinpoint what would be the problem..we keep blamin git on the bathroom plumbing. This is a rental house now and i'm getting ready to show it and that's always a drawback for rentals...help.

I am noticing a sewer odor coming from our main level bathroom. It seems like it is the bathtub that has not been used in the 7 years we have owned the house. We also notice this smell in the upstairs bathrooms, but it is most noticeable when entering our home so I'm thinking that is the source.

I finally found a group that understands a sewer odor in the bathroom. I live in a 42 floor highrise on the 17th floor. We will be here a year soon and the odor started in Jan. when several pipes in the building burst and caused a lot of issues in the walls of the building. I started to notice the smell of urine. Sometimes light and at other hours stronger and now seems to hit late afternoon through the night. It drifts out to the other rooms. I've had the building maintenance crew out here and they tell me nothing is wrong, they checked the seal on the toilet, the shower and the sink drains etc. Same answer every time, we can't find anything wrong. We are at our wits end living with this odor. At times it smells like a public toilet. We lease in this building and it's very well kept but I'm frustrated that they don't seem to take this issue seriously. What can I do to solve this problem? HELP!

"What can I do to solve this problem? HELP!"

Maybe start a thread asking for help? ;-)

I'm not sure how to start a thread on this site. Since I wrote this the building engineer said he found a vent fan for our tier was not working and had it fixed and checked the main vent on the roof and it's fine. He said I should see the odor disappear. Well, I waited 3 days and it's every bit as bad as it was. I'm just so frustrated...

I seem to have an exact symptoms of sewage smells in the morning and evening the past few days. I too thought it is some venting issue and sent water down the vents from the roof hoping the problem will go away. This is happening in the master bedroom and more in the walk-in closet next to it which has a attic vent too. I have already gone to attic vent to find the issue and could not smell much during the day(will go again after reading this thread). The smell today morning seem to come from the wall in the closet which shared by the wall opposite the bathroom sink and not sure why. My wife noticed some rat dropping just last week and now suspecting that it could be the dead animal reading this thread.

However I am not sure how I could find this rat if this is the cause. Could it be stuck in walls? Any help would be appreciated.