I use Oxi-Clean on fermenters, both beer brewing and wine making. After rinsing well, I fill them with water, add Oxi-Clean and soak over night, scrub and rinse well the next morning. Be careful with some off brands of oxygen cleaners as many have various detergents in them with low levels of oxygen cleaners added. I don't like "One Step" cleaner as I have had problems with it leaving a hard to scrub off/out crusty residue if left to soak for more than a day. I agree, TSP seems extreme but lets see what other say...
Tony