Sewage smell from basement and main level

For the last few months I have been smelling strong sewage gas in the basement and the main floor laundry room. Here are the all the clues, some may be irrelevant...

- I have a house that is 10 years old (all PVC plumbing and venting).

- I checked ALL the drains, all have sufficient water in the P-traps including the evaporate drain in the furnace room and the washing machine drain.

- I have two vents, both were checked for blockage from the roof top

- The basement and the laundry room are the only two areas of the house that DO NOT have air return to the furnace.


I tried putting bleach, vinegar, and baking soda through the washing machine cycles to no avail. My basement is finished so it is tough to check the vents for any cracks, but I dont see how the pipes could have cracked in the last few months on their own inside the walls. ANY IDEAS????

do you know where the pipe in the wall for the washer is? looking for a clean out plug that was left off.?

can you explain the evaporative drain you speak of to me..take a picture

Do you have any rough plumbing in the basement?

As far as the evaporator drain, I just mean the drain near the AC and furnace unit. Its flush with the foundation concrete floor, I believe its just a drain for the AC unit and furnace. No rough plumbing in the basement, It has been finished, and when the house was built, all the vents and drains were preinstalled

if the ac is not running no condensate will go into the trap, the trap will become dry during winter mths

and stink. this is probably your problem

are you sure the smell is not just funky musty mold basement smell

also,,what type of washer do you have. some of the newer washers [the front loaders,] drum smells