The former owners of our log home ran all gray water (showers, washer, sinks) through PVC pipe that runs under the house in our crawl space and empties out into the woods behind the house (we're on 5 acres of hardwoods). Toilets are emptied into the septic. There is an occasional sewer odor in the vicinity of the washing machine drain. As best I can tell, the drain pipe runs down into the crawl space and connects directly to the system running outdoors. I see no p trap or roof vent pipe. Since there is no sump, no sewer line and no septic connection, does anyone know what would be causing the smell?