Have a question for those who have used electrolysis to remove rust from steel parts, particularly those with closed interior access, such as fuel tanks. My FJ60 fuel tank had a thin layer of rust inside. Not bad, but enough that the loose rust powder was clogging the filter. I removed the tank and have used/am using electrolysis to remove the rust. It worked great, just one problem remaining. The rust is gone and now there is a black coating on most/all surfaces. I have read other accounts of the same thing, but in all the other accounts I've read, it has been on things like tools or valve covers or other parts where one could easily scrub the black coating with a stuff brush and rinse, to be left with a squeaky clean surface. However, there is not access to 99% of the inside of a fuel tank, so I am wondering what others have done to remove this coating without the ability to get in and scrub with a brush. I can scrub very small areas away through the various openings in the tank and the black coating comes off easily with something like a toothbrush, agreeing with what I've read in other accounts. But, it won't come off with simply a rinse of water (fill fuel tank with water and drain). Ideas or personal experience?