Sewer gases are made when waste materials decompose in the sewage system. Sometimes the odour comes from septic tanks, while other times, it comes from public sewage systems and drains. The smell can be toxic to breathe, and is also explosive, due to the methane contained within. Plumbing drains are made to keep the gas inside pipes, and there are vents on top of most houses that vent the trapped air out. Sewer odours may occur due to cracked pipes, leaky drains or bad vents.
Lift the lid to the toilet and see where the water is sitting. If it is sitting below the back lip of the toilet drain, you more than likely have a sewage leak and the water is escaping through this area. Consult a plumber to track down the exact area of the leak or crack.
Check the sump pump for odour, as this can be a major source of smells. If the pump is not emptied on a regular basis when full, the water will become stagnant and emit an odour much like the smell of sewage. Empty the sump pump according to the instructions for your particular model.
Check your vent pipes on top of the house. Leaves and debris often clog vent pipes and create a sewage odour that lingers in the home. If this is the case, use an automatic snake to clean out the pipes and remove the clog.
Open all of the windows in the affected area once you have corrected the cause of the sewer smell. Place a window fan in the window with the side that blows air facing out. This will help suck the smelly air out of the room.
Clean the entire room with a household cleaner, or mix one part bleach with three parts water to create a sanitising cleaner. Be sure to wash down the walls, as they may hold onto the smell. Remove all cloth materials such as towels, rugs and shower curtains. Wash these material to remove the smell.