We have had an odor for a few months now coming from the basement. We have added bleach & water to all the drains in house hoping that would fix it. We add water daily to drain in basement floor to help the P-trap drain effectively. The smell comes back when weather is above 40 degrees. The fumes come through the return air vents in living room & dining room and smell there as well. We had a roto rooter repair man come out and check for leaks... he found nothing. What should we do at this point? It's pretty bad fumes that stink at this point... Thank you.