Last summer, I started to have a methane/sewage smell in my home. I called a septic plumber and they replaced my pipes under my sinks in the kitchen and laundry room, added an extension on my vent pipe, and closed off an old vent pipe that had broke in the wall as well as added goosenecks on my two sinks. The smell went away for a brief time. There is no smell in the winter, just the summer, which leads me to question the a/c. It is draining correctly, but it does drain under the house. This summer, the smell is back and still strong. I am not sure what else to do? The plumber came back and checked and said the plumbing appears fine, re-drained my cess pools, check my lines, and said it was carbon dioxide. I called the gas company, and they said it is not carbon dioxide; however, it is a sewage/methane gas smell. I am at a loss and I am starting to have sinus issues. Please help if you can!