Remove plug, crack open drainvalve and open res cap. After my right-most tube is drained i remove that so i can blow into the upper right radiator. Which will force the liquid out of my system. Works great, gets out all of the liquid.
Honestly its a lot harder to drain the water from the radiators rather than the loops.
I like that, maybe i should do that instead? But wouldnt it look quite...conflicted?