Just another build thread - Sort my combo!

Doable, but hazardous. I do sometimes on a small scale. How large of parts are you wanting to clean? And the waste from it is another matter altogether. Lots of protective eye wear and long rubber gloves, and a chemical apron at minimum. Keep a couple of 2 liters of seven up handy to neutralize spills or accidental contact. You cannot be too careful with this stuff, it’s one of the worst chemical burns you can get. Sodium hydroxide works best on petroleum greases and oils, the potassium hydroxide is more used to emulsify animal fats and grease. So you are correct to use bulk crystalline caustic soda. The saturation point in water is a fifty percent solution (2 parts water by weight to one part caustic) which will eat cam bearings and aluminum anything. And you want to keep it around 120 degrees or better when it’s being used. If it’s for cylinder heads and smaller items you could make a smaller tank and get a couple of old tabletop stoves to set it on. When it gets grimy, skim out all the solids and mix with kitty litter and oil dry before bagging for disposal in garbage. Best way to buy caustic:
https://www.amazon.com/Devil-Sodium-Hydroxide-Chemical-Caustic/dp/B00KCY6N28/?tag=fabo03-20