Pulling a knock sensor would drain the block, that's why they say to do that.
If you really want to flush everything out just remove the upper rad hose and thermostat housing. Stick a garden hose straight into the lower intake manifold and take the rad cap off. Start the car and let it run, it should flush just about all the coolant out.
Even pop the lower hose off the water pump if you want.
Then dump a full bottle of coolant into the lower intake manifold thermostat hole, fill it up with water to the top, stick the thermostat back in. Top off the radiator with coolant and water, let it run. Test the strength of the coolant bleed as required.
