I live in a 50 year old ranch with an upstairs for 4 years now. We get a sewer smell through the house consistently. Not every day but maybe once a week. I have tried to put bleach and other products in my sewer drain, which is right on my laundry room floor located directly next to my kitchen. It comes back. I have a small laundry room which contains my sewer hole on the floor and my furnace is also in there.
Answer:
That sewer smell could be coming from the floor drain. You might want to check that out because there is a trap under it like you have under the sink and if that pipe is broken, water that goes down just soaks into the ground but at the same time, sewer gasses, which it is supposed to be there to block, can migrate up into the house. You can't block it so if that's the problem, get a plumber unless you're prepared to break up the concrete in that area, do the repairs and then re-pour.
