used one of the tools that was designed for it but added to it. It was the kind of tool that had two round pins that went into two holes in the top of the cap. It was/is a bronze deck fitting tool I got from West marine that had the two SS pins. You could turn it over for different sized cap holes. I took a two foot long piece of 1/4 X 1 inch flat stock and drilled two holes in it to match the pins in the tool. This kept the pins lined up to the holes in the cap and increased the leverage enough to be able to break it free with steady pressure. Maybe this might work for you also. Actually, as I remember, I used the anchor winch handle.