I would consider returning the Dex and buying "mixes with any type, any color" coolant instead. Removing knock sensors is the best way to get most of the coolant out of the block, but is not easy to do. The sensors are fragile, very hard to get out, and must be replaced without losing the ground connection, water seal, or over-tightening.
I don't like to use the radiator drain valve because they often fail to re-seal once they have been opened up to drain, requiring replacement of the drain valve assembly. I find it quicker and easier to wiggle the lower radiator hose off just enough to control the flow of coolant into a pan.
For some other ideas on how to flush the cooling system, use the search feature at the top of the page and use the keywords: reverse flush.
Here'* one I found doing just that:
Originally Posted by bill buttermore
...filling at the thermostat opening as described in the Techinfo article is still a good idea.
If you have the time, and energy, and have a nice warm place to work with a sanitary drain nearby, you might want to try this method for flushing. http://www.bonnevilleclub.com/forum/...ic.php?t=84203
Following that method, you will perform a true reverse flush for the radiator, engine, and heater core. Using the flushing Tee alone will not provide a reverse flush for the heater core or for the entire radiator, just the side tank on the passenger side.
Reversing the direction of normal flow through the system is more effective in flushing sediment from narrowed and blocked passages in the system than flushing in the normal direction of flow. Normal flow is from the bottom of the radiator to the water pump, from the water pump to the engine block both sides, up into the cylinder heads and intake manifold, out of the intake manifold passenger side through the coolant elbow, to the heater core through the top heater hose, back from the heater core through the lower heater hose to the water pump, out of the intake manifold driver'* side to the radiator top hose through the thermostat (only when open) across the radiator from the driver'* side to the passenger side, out the bottom of the passenger side tank.