Okay, it is not as bad as the headline makes it look but, if you understand what you are looking at here, this is a pretty evil arrangement. Prior to the home inspection, it was mentioned to me that the bathroom had an "off smell." This is the attic view of the home over the bath. Off to the left, the white flex duct, is from the bathroom fan. What is it attached to? You assume it vents out through the roof or the side of the house, right?. Wrong! This vent is spliced or cut into the sewer vent system. And this was a septic system in grave need of pumping. Over to the far right, that vertical pipe going up through the roof, is the sewer vent stack that is normal on top of the roof. This was a very unhealthy situation. When the bath fan was running, it would force air up into this system so the smell did not come into the bath -- too much at least. But, the moment the fan was turned off, the odor from the sewer was seeping back into the bathroom through the white flex duct. This is yet another good reason for someone to have a home inspection. Also, this is a really simple problem to solve, but to do so, someone has to recognize what the problem is.
Thanks for looking,
Steven L. Smith