I was the third plumber to investigate this smell...or where it was coming from. Needless to say, it was getting sucked into the duct work and spread all over the house leading to irregular pattern/locations. Intially I was going to do it myself, but the cramped space, and weight of the material, time, dictated otherwise.
I can only speculate, but by the splatter marks on the duct and the dry, airborne poo, they must have had a backup, and possibly the rodder opened up the hole. But who really knows?
The photo of the flashlight kind of gives an idea of the cramped area. Also, my partner was on the otherside of the duct, that way I did not have to crawl all the way around on my belly and snap that.
There were two combos, I cut them both out, then replaced with no-hub.