A dead leg is where an ancillary flow "T's" into a main flow channel (see
attached drawing). Normally no flow exists in portion of the T because
there is usually a device in the branch designed to stop flow. Stagnant
water may result from this restriction and therefore provide an
environment for microbes to grow. Dead legs may be vertical or
horizontal. The distance between the flow stopping device and the
centerline of the main flow channel is defined as the length of the dead
leg. The length of a dead leg should be as short as possible, but may
not be greater than 6 pipe diameters as measured from centerline of the
main flow channel to the shutoff point of the flow stopping device.
Diameter is the smallest pipe diameter in the configuration. Must wash
through all valves on all dead legs to remove water. All dead legs must
be completely drainable and sanitizable.