We live in a double-wide, out in the country. We had a new septic system installed about Christmas time, the old system had a "failed field"... The old system had the tank about 60 feet from the house and, when they dug it up, the drain line from the house to the tank had a "dip" in it that trapped water. The new system has the tanks installed about 5 feet from the house and now we get a VERY strong sewer gas smell out of the roof vents of the house. I realize that to=hose vents are supposed to vent gasses and such, but the wind blows that smell right into the yard and it STINKS! I talked to the installed and he can't explain why it smells now, nor could he suggest a cure. I think it smells now because there is no longer any traped water between the house and the tank. I was under the house last week and noticed that there is room under there to put a trap of some sort to capture some water and prevent the septic tanks from venting out through the roof vents. I could build a "P" or "J"" trap from 4" pipe to trap some water. Three questions: Would this be legal and/or smart? Would it work? Would it cause drainage problems with the toilets, etc?