Denatuered alcohol will work fine, the shop manuals suggest using that to flush the brake system. Just fill the m/c after you remove as much of the fluid as possible, and then have a helper gently pump the pedal as you open the bleeders. Pressurizing isn't necessary. Do this 2-3 times to get the lines cleared out, then fill with clean fluid and bleed the system. You will have to go around and bleed it 2-3 times to make sure that you have all the alcohol out and have only clean fliud at the wheels. Also do not use DOT 5 fluid. I tried it and I had problems with leaks in the master cyl. and front wheel cylinders. I had to flush the system to get it all out and put in DOT 3 fluid.
