Does anyone really do this to their cooling system?

my68barracuda said
I have doubts that the “owners manual” instructs one to remove the freeze plugs to drain the antifreeze. It’s not that I don’t believe you, it’s just that is insane.
The hex head plug low on the block under # 5 sparkplug is the drain for the water jacket. Get that threaded plug out and you will still probably need to probe the hole with a stiff wire or screwdriver to punch through the rust and crud to get it to drain. Thread the plug in hand tight re fill the block with clear water and remove the plug several times to get it flushed good.

Here's the excerpt from page 43 of the 1974 Plymouth Duster Owner's Manual. Perhaps I've misunderstood it. It says to "remove the drain plugs in the sides of the cylinder block". I took this to mean the freeze plugs because I can't find any "drain plugs" in the side of the block. So now I'm assuming that they are referring to the single plug that I posted a photo of. I guess what I'm wondering is if you do a better flushing job by using the backflushing tee instead of draining the block like the owner's manual says. To me, it seems like using pressurized water to blow everything out of the cooling jacket is better than simply using gravity to drain coolant out of a hole. Your thoughts?