Leaves and vent pipes

We had an interesting service call recently where the plumbing vent goes sideways in the attic for a while before going through the roof. The owner started to complain of sewer smell in the house. What we eventually found was the horizontal section of venting in the attic was packed full of leaves. We had to cut the attic vent piping and install cleanouts in it in order to snake the vents. This probably would not have happened with the old code which required full size stacks, but the new code goes by minimum sized piping. In the picture you can see where we cut the pipe and the dark area in the middle of the white PVC pipe is a pack of wet leaves.