When flushing a rad, I use a garden hose, and use whatever I have to hand to try to seal it to the either the flow or return connection to the rad, and with the rad cap in place I turn the hose on full and flush till the water comes out clean then connect the garden hose to the opposite end of the rad to reverse the direction of flow. Carrying out this process a few times till no discolouration in the water worked well enough for me over the years..
