Thanks for all of the info and suggestions. Creek side, I agree that it is probably the septic system. And we are now fairly sure it is caused by the roof sewer vents freezing up. Most often the smell has gone away after my husband broke through a thin layer of ice on one of the vents. The reason we thought it might be something else is because our plumber told us that a thin layer of ice usually doesn't cause sewer gas to back up, and he also said he didn't think it smelled like sewer gas. But what other explanation could there be? Why else would the smell come and go so often, if it isn't the sewer vent freezing and thawing? Last night confirmed the fact, at least to us, that the smell is coming from the freezing vents. It was seriously stinky last night and much more of a rotten egg sulfur smell. So DH went up to the roof and knocked ice off of one of our vents. This morning, the smell is pretty much gone. So if the smell is the result of ice forming on the vent, then does anyone have an idea of why our one (not both) roof vent is freezing over at least 3 times a week? And how can we prevent it so that DH isn't climbing on the roof so often? Why have I never heard of people having to unplug their sewer vents so often? It seems that something must be seriously wrong for that to keep happening.

That was caused by not seasoning at a high enough temperature......all you accomplished with your seasoning attempt was to create an oil removable coating on your pan. That is not the same thing as actual "seasoning". Next time you you re-season your pan with Crisco, do it a higher temperature.....350 degrees is NOT HOT enough. For best results you need to use a temperature that is ABOVE the smoke point of your seasoning oil (Crisco in your case).....use a 450/475 degree temperature instead. Make sure you put a VERY thin/light coating of "melted" Crisco on your "warm" skillet. You do not want the Crisco to be puddled or in a thick layer anywhere on your skillet. Again, use a very thin layer and place in a hotter oven. You will have to do this coating/baking procedure several times for the pan to develop a real nice durable seasoning. Dan

Thank you. I pulled everything out. It wasn't that difficult after heating the outside of the CI pipe for a minute. I'm glad I did because I saw a big boo-boo. When I first put the pipes together, I though that putting a little oakum at the front of the pipe might make a nice gasket in case the PVC didn't reach all the way back. I created a nice clog in the pipe before we had a chance to use the toilet! So, I'm sure that contributed to why the water was trying to get out around the pipe. So, I bought a donut from the plumbing supply store and used that. I soaped it up real good and put the donut into the cast iron first. I tried putting it on the PVC first, but that didn't work because since it was soaped up, it was just sliding up the pipe when I tried to push it into the CI. I had to use a 3LB hammer to get the PVC pipe into the donut. I'm not going to glue all the other pieces together until I'm sure that this isn't going to leak again, but I feel pretty confident that it's good now.

Can I get in on this conversation with a question? I have something similar in my 22 year old house. It is three stories. We do not have city sewer. We sometimes have a sewer gas odor that comes up the vents in two bathrooms only. They are exactly on top of each other. We have had a plumber out to the house three separate times. At first he said make sure to keep traps wet. We did that, smell sometimes comes back. He came out again, same thing and checked everything. Last time he said that all fixtures go into one large vent pipe on roof. Husband got up there and sure enough only one for 4.5 baths, washer, etc. The smell is only in these two bath areas. There is one bath below these two exactly as well. He said tub downstairs is not used much and trap could be dry. He extended the vent pipe up several feet in the air. He said sometimes when weather system moves in, it can hold gases down. We have absolutely no idea what this could be. It only happens every couple of weeks, but when it does, it smells so bad. We have also smelled this outside once or twice and it was so bad, I was so embarrassed. We were gone one week and our friends walked by the house to make sure everything was okay. They said they thought something BIG had died there and they actually walked around the back of the house but could not find anything. Please any thoughts. Desperate in NC