Sewer smells in the basement happen to more homes than you think. Some of the causes can be a cracked sewer pipe, as well as floor drains, sewage ejectors can leak, and showers, toilets and laundry can off this odor as can private septic systems.
To inspect a home sewer pipe, put on a pair of gloves and run a paper towel on the sewer pipes that are above ground to see if they leak. If the paper towel is covered in sewage, call a plumber quick.
To inspect the floor drain, shine a flashlight down the drain and make sure that there is water in the elbow. This is very important. If there is no water in the elbow, you need to pour water down that drain to get rid of the smell.
For those who have toilets and sinks in the basement, oftentimes the sewage goes into a basin in the basement with a sealed cover. Locate that cover and flush the toilet. Then feel around edge and see if you feel any water or air movement. There are kits to make these airtight.
To inspect appliance drainage, be sure there is water in the trap. Without the water in the trap, the odor can come into the home. If you have a plumber come to the home, you can have them check as well.
To check on your underground private septic system, go to a plumbing supply store where they sell packets of dyes. Take a dye packet and flush it into the toilet. If there is a crack in the sewer pipe you will see the color seeping into the foundation. If you see this, call a plumber quickly. This is an expensive repair, but it will eliminate the odor.