I got a call the other day, Where the caller was complaining that there was an odour coming from the guest bathroom, "like a sewer smell" he said. When I inquired if there were any appliances that had not been used for a long time, he said that the tub was not used since he moved in. I told him that was the problem. The water in the trap had dried up and was then allowing the methane gas to get through the drain into the room.

 

You should check all drains in the house each year to ensure that you see water sitting in it. Especially the appliences that are rarely used like the floor drain in the basement or the Laundry tub (some do not have the washer drain into them).