Hi new question. Neighbor has a summer home closed up for weeks at a time. Septic gas coming into the house. We have checked all the traps and made sure they had water. Now here is the strange part. The builder did not use a vent through the roof. He has those one way vents in the attic that allow air to enter when system goes to vacumn when you flush or water drains down pipe. Can't really smell the gas in the attic and no smell in the crawlspace where pipes exit house to septic. One individual has suggested that because of pressure changes due to weather change the septic system is "burping" the gas into the house from the tanks. I have trouble accepting that the tank is that tight and no air can get in or out. It has the normal square tapered concrete cover and then a plastic chamber above with it's own plastic cover ( no dirt blocks access). Just think it should be able to "breathe". Any suggestions would be appreciated.