Re: Backup from washing machine into kitchen sink
The venting occurs above the roof for two reasons. One is odor- above the roof it dissipates quickly and is rarely an issue. Second and most importantly is that sewer gasses can be poisonous and contain nasties which can lead to another obituary column.
Many old houses here have the entire drain stack (including the vent) ran on the outside of the house. While not pretty, it works. You really need to vent above the house somehow. So long as it's within 40ft laterally of the fixture being vented and there is an upward pitch toward the vent, you can locate it anywhere in a convenient wall where repairs are easier, such as in an exterior closet wall. At the top plate line it can turn so that it either clears a couple feet above the eaves or so that you can run it through the roof. It's not that tough to do and one vent can usually serve all fixtures when it's done properly.
Studor vents are to be used only where proper venting is practical impossibility such as with a sink in an island. They are not to be used as a stand-in for a proper vent which is where this problem comes from. Get out the drill and holesaw and run a proper vent before someone gets deathly sick.