Occasional septic smell when washing machine is used
Our house is a 3 year old split entry with the laundry room in the basement. In the last 2 months I've noticed a strong septic odor coming from the laundry room but only once in a while... maybe every 3 out of 7 washes. The septic tank (1000L) was pumped in September and this is the only area in the house where the smell is located. The smell, when it comes, disappears after a few hours. We have all the proper plumbing connections, p traps, etc. I've tried putting vinegar in the washing machine (full cycle, hot water) but the smell keeps returning. We do have a vent on the roof of the house, it is all up to code and isn't blocked. Can you think of anything else that it might be?