Discovered that after having done the boiling dish soap trick - a heavy layer of baking soda, then dump vinegar on top. Do outside, it makes a mess!
Nephew and I were working out how much of both to use to make a science fair volcano, and I was using the old, couldn't clean out, may as well trash it pot to contain some of the mess. We'd gotten out the volcano amount sorted, then because he's 7 and I'm not exactly mature either, we dumped the last of the box in, then poured the vinegar over top.
Hilariously funny mess, and a clean pot.