HI. We have a sewer smell that comes and goes in the house. It started in the downstairs bathroom and then it moved to the upstairs bathroom. We had the septic tank pumped and the smell was gone. Then it came back 2 weeks later very bad. Now its every where. Both bathrooms, back laundry room, out side under the deck?? And sometimes through out the other rooms in the house. We use all the drains daily so I'm sure its not a trap that water has evaporated from and I can't smell it coming from any drains. I climbed up on the roof and the vent is not clogged but the smell is 10 times worse up there. The strange thing is the crawl space does not smell at all. I went down there and checked all the drain pipes and didn't see any problems. What should I do? I am out of Ideas. Please help!

Also all the drains work just fine none are slow and none gurgle. The toilets both flush with no problems either. Thought I should add that.