I did some more research too, and sort of came up with your conclusion as well, that they
all appear to contain ethanol, and that ethylene glycol is toxic, and propylene glycol isn't.
So if I get the pink stuff, and the container says "non-toxic" it's probably propylene glycol based,
and is safe to use, and theoretically drink, although I don't treat my fresh tank with it, just my
waste tanks and toilet/sink traps and valves.
Thanks for the further investigation.
Sometimes the simple stuff gets away from me.