Our home is about 25 years old, and has a laundry center on the second floor. During the last two heavy rainstorms a strong septic tank odor has developed in the laundry area and the hallway just below. The septic tank was pumped in the last year and there is no smell outside the house. What would you suggest to attack this odor? Where can I look myself, and at what point do I call a plumber?
Not knowing the plumbing layout, I can only suggest a couple of ways to go about this. First I would try plugging the pipe when it rains, if this solves the problem then your trap is going dry, this could be caused by vent blockage, trap going dry by a wicking action ( as lint or something in the trap soaking the water and drawing it out to the waste line. You could hire a plumber to smoke test the system, this could possibly locate a broken pipe etc.