Our basement gets this very bad sewer odor. My husband has checked everything that he can think of what could be causing the odor and we had our septic tank emptied, it wasn't even full and the guy told us that couldn't have been the problem. Our house is 6 yrs old and we purchased it 1 1/2 yrs ago. Ever since, about once a week we get this putrid odor that lasts about 2 days. We cleaned out the sump pump hole, which wasn't dirty, added bleach to it to see it that would help with the problem, but it didn't. We have a toilet downstairs, but it seems to be that everything was done to code when they installed it. We just can't figure out where this smell is coming from.
Answer:
I wonder if there's a sink or toilet that is more than six feet away from the main stack. If there is, you can be sure that every once in a while, when a toilet is flushed, it gets starved for air and draws water out of the offending fixture's trap. That permits sewer gasses to migrate back into the house. A dryvent will rectify that. I'm going to suggest also that you cover the sump hole as follows: Sump holes should be fitted with covers which have weather stripped holes only large enough for the various protrusions (pipes, wires, etc.) through them. Three-quarter-inch plywood makes a good cover and if the necessary holes are drilled in a straight line, the plywood can be cut to fit around all the protrusions, the edges of it properly weather-stripped and put in place. This keeps an otherwise large surface of water from evaporating into the basement and substantially raising humidity and odour levels there.
