To limit the probability that blockages in soil-or-waste pipes that are served by yoke vents will lead to the backflow of sewage into vent stacks via yoke vents, which could lead to blockage of the vent, which could lead to a reduced vent capacity, which could lead to siphonic action or back pressure in drainage systems, which could lead to trap seal failure, which could lead to the entry of sewer gases into occupied space, which could lead to negative effects on indoor air quality, which could lead to harm to persons.