I use a far more scientific approach when using my oxy clean free. I fill my carboy half full of hot water, use about half a scoop of the measuring tool that comes with it. Shake the crap out of it, use my carboy brush to scrub the sides, rinse with hot water at least 3 times or until there are no more sudsy bubbles while filling the carboy, let air dry, cover the carboy mouth with a stopper and let sit in my storage area until brew day.
I do something similar with my carboys, but because they are plastic I dont use a brush. I fill with enough hot water that when I turn it upside down into a small bucket of water the oxyclean liquid is above the krausen ring. I let it sit overnight then rinse. Usually the ring is gone by the next morning. I also use just enough oxyclean to just cover the bottom of the scoop even when I am soaking big buckets. The small amount still works just fine and it seem to rinse off easier.