Does anyone really do this to their cooling system?

but they are refering to the drian plug. big allen headed or square head gub screw, not the core plugs

one presumes this is an early version of cut and paste
the same text appears in my manual published in Austrlia and mine has 1 drian plug, plugs is inaccurate in my case.

the core plugs were there to fill holes that were used to remove casting sand after the block was cast... i have some in my clinder head as well
early heads had screw in plugs my later head has minature core plugs between the rocker posts and valves

mine isn't a slant.. mind