Systems & CodeQuestion 35 of 110
A building drain serving fixtures below the elevation of the public sewer manhole must be protected against sewer backflow. Which device is required on that low-level drainage?
a.An air gap
b.A vacuum breaker
c.A backwater valve
d.An air admittance valve
Explanation
Fixtures below the next upstream manhole rim are subject to backflow from a surcharged sewer and must discharge through a backwater valve, which closes when flow reverses. Fixtures above that level must not drain through the backwater valve so they are not blocked when it closes. Vacuum breakers and air gaps protect potable water, not drainage.
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