We have a sewer smell coming from the washer drain in the basement of our new home. It becomes most prominent when washing and then afterwards.
The house is about 30 yrs old, two levels with the basement being mostly underground.
We have also smelled the odor outside the house as we added a vent pipe filter on the roof which seems to have helped the odor outside.
The house sits on a hill with the septic and drainage fielded flowing down hill.
What can we do next to eliminate this bad odor??

Try This. Pour 1/2 gallon of bleach down the washer stand pipe and let it set for 8 hours. Then cycle the washer to flush it out. Smell better now? Regards, Tom