Excellent point 64. I perfrom the "derusting" outside. The parts I did were like brackets, trim peices, and bezels. Technically, you want your electrode to surround the peice your working on. Sometimes thats not possible. so the best thing I did was to get the object as close to the electrode as possible. This insures good current flow. The better the current flow, the better the process. As for mix ratios on soda to water, I only used like a half a cup for that 5 gallon pail. Worked fine. I don't think the amount of "detergent" is critical, it's the proper flow of electrical current thats key.