We are smelling sewer gas whenever we take a shower or wash clothes. We have a septic tank and I know there is not a trap between the septic tank and house. The gas smell is coming from the vents on the roof of the house. What can we do to fix this?

Actually, that's where the smell SHOULD be coming from. There wouldn't be a "trap" between the house and septic tank. One clue, however, is that you smell it when the hot water heater is on-showering and washing clothes. If you don't have enough makeup air or too tight a house, you may be backdrafting down the heater vent from the sewer vent. Try extending the vent pipes and see if that helps.

We only smell it outside except when the windows are open so it sounds like it is working correctly. I do like to have my windows open so is there a way to get the smell away from the house?

Yes it is working properly. I thought you were getting it inside and didn't consider an open window. It's 40 in Atlanta. You could extend the vent as I suggested. It is probably PVC or ABS. . Find the pipe diameter and get a connector and a piece of the same size pipe. Cement it on. Try adding another foot. When did you have the tank pumped last?

Brian is correct, that vent stack is doing exactly what it is supposed to be doing. Any of us can get a odor under the right wind conditions or atmospheric conditions.

This is a new house, just moved in in October. The roof is steep with a lot of different levels. Could it be that the vent is on a lower level of the roof ( I will have to see if that is the case) and it causing the smell to "stick around"?

One problem with multi leveled roofs is that a vent on a lower level is "enclosed" by roof levels at a higher point. Air will wash down from high to low, particularly when cold or windy and cause down drafts. You might want to try mobile home vent caps. They allow the vent to work but limit back draft with a baffle. I have used them to keep debris and acorns from falling down the vents. This may be an unfortunate case of vents, valleys and prevailing winds and you may not be able to solve this easily. You could also see if a lower vent could be configured to go through another attic space and vent higher up.

Lowe's Website:Vent caps designed specifically for mobile homes. Galvanized construction. Complete kit.

Galvanized steel
2-3/8 In. diameter
For 1 or 2 In. vent stacks
Designed For Mobile Homes
MFG Brand Name : DANCO
MFG Model # : 88182X
MFG Part # : 88182X

Thanks for all the information and ideas. We will have to look into some of these solutions. I appreciate all the help.