Well, I finally had a chance to "tour" the septic area last night. No stink from the thank lid or the four 4 inch pvc "vents" comming out of the ground in the drainfeild. A post or two here said the pipes in the drainfield are inspection ports and should be sealed. Mine are most definetly vents, They have a vent cap on them. No smell from these either. The idea that the smell is comming from the roof vents is getting more and more likely.