Cooling system

Okay, I installed a frost heater yesterday, and I noticed that the coolant is brown and muddy, meaning the po ran the wrong anti-freeze at one time or another. This kind of irks me because I specifically checked the coolant reservoir before I bought the car to make sure it was pink...so I guess now I need to flush the system to get the crap out of there. How do I achieve this? The petcock on the bottom of the radiator will only drain the radiator. It is only safe to do the job with the engine cold. I guess that means I have to pull the thermostat? Anyone have any advice? How much coolant does the entire system need?

I read here that pulling one of the hoses off the oil cooler will drain the block, but I have no experience doing this.

Drain what you can from the bottom of the radiator. Use distilled water to fill it up and warm up. Drain again and use the distilled water again. Do this until it's comes out clean. Drain the last time and add the correct amount of VW antifreeze. Then top off with distilled water. Hope this helps.