Plumber's Guide #10 is correct; I am RH.
But, let me describe what I found with my 5 year old NG tank-type home water heater. The homeowner's manual that came with the new house recommends "draining" the water heater annually, and in fact the AO Smith instruction manual from that year also describes a draining procedure. I kind of slacked off in the first two years of ownership, then had a plumber I hire for jobs I don't have time to do drain the WH while he was here to work on another task in 2017. He also replaced the sillcock valve on the tank drain with a straight ball valve at that time. Since not much sediment came out in 30 minutes, I procrastinated until 2019, and had the same guy drain the WH while he was here to check the anode rod for the first time. Again, not much sediment in 30 minutes. Today, about 17 months later, I took charge of the "draining" myself. After about a half hour of draining, I was still getting a small but steady volume of mineral sediment out to the tank, as confirmed by holding a kitchen strainer under the hose output, so I opened the CW valve a little at first. When that caused heavier sediment to come out, I opened the valve all the way, and it was like a snowstorm coming out of the hose end. I had to let the system run wide open for another hour before the flush water ran clear. Tonight, I checked AO Smith owner manuals available on their Website, and found that they now provide instructions for "draining and flushing," instead of just draining. Although the new instructions don't describe flushing at full water pressure as long as I did, I believe that my episode was an anomaly, due to waiting too long between drainings, and inadequate draining procedures. I'm confident that the next drain and flush will take much less time (and water). So the point of my story is that draining alone is really not enough to completely remove what sediment can be removed in areas of hard water, like mine, especially with a home water softener, and flushing is a must (as the manufacturer now recommends).