Draining shouldn't be a big deal. Open the drain valve and if water doesn't come out then open a vent on a radiator and water will come out.
If you wanted to get creative then use air to blow the water out of the system. Be sure and keep the pressure low, less than 25 psi or so. The advantage to rigging up an air system is that you can use air to check for leaks before putting water in the system. It'll save a lot of mess. Don't ask how I know that.