All I can say is: wow!
I finally tried it tonight and it works as advertised (which is a rare thing these days).
I did use hot water from the tap to preheat the drains (as per usage instructions) and used the same hot water to dissolve the crystals. After the waiting period (not timed but more then 1 minute) I flushed with boiling water followed with several more minutes of hot water from the tap.
The drain turned from painfully slow into a scary sounding gurgling monster that can't get enough water --
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