I have been in my townhouse for three years. Each time summer rolls around and I turn on my air conditioner, the house fills with the smell of sewer gas. This doesn't happen all winter long. I have had the sewer rodded all the out to the street. A camera was put into the line and I was told that there is a belly in one of the drainage pipes. I am assuming that the waste sits there and sends the odor back into the house. I have started to pour water down the trap in the basement and this helps for awhile. Is there something that I can use to neutralize the smell? (I have tried bleach, Lysol etc.) I can't afford to tear up the driveway, as was suggested. Thank you.
Shirley

Make sure that all of your traps are kept full of water, if you have a shower that you hardly ever use make sure a little water is run in it every few days. The water in the trap in the basement could be drying up faster than you are refilling it.
There is a drain pan in the bottom of your evaporater coil, and I am assuming that it is sitting on top of your furnace, this pan drains off the condensate that builds up on the coils. This pan can get very cruddy and create a very bad smell, most of the time this is a musty smell other than a sewer smell. Cleaning this pan is almost always something that a technician will have to do.