I searched for this and still couldn't find anything....
I have drained the engine block and the rad is draining still... I was wondering if you have to take the res off or if you just let it drain through the rad ?

I have been running mostly water because it eats coolant but since it is getting cold I decided to drain/flush and start using coolant.

 

The reservoir won't "drain through the rad", if you want it empty you'll have to remove it and turn it upside down.

 

If you have been running straight water, you can kiss your heater core goodbye this winter. Once, on a different car, I had a radiator leak and I was lazy and just put water into it. It rusted my heater core from the inside out.