Backyard Aquaponics
A place to discuss aquaponics

I would think the residue is mostly caked oil. Perhaps a soaking in water before scrubbing with soap would also help. If it is stubborn, let it soak in soapy water. What ever you use to clean, just rinse real well...it will be fine. Vinegar you can use full strength for cleaning, any amount of water will rinse it off. Bleach I would dilute with water as it is not good for the skin at all. A cup of bleach to a 1/2 bucket of water or so makes it somewhat safe. Still when cleaning with it though, wear rubber gloves and protect your eyes. It is not a bad idea to get in the habit of wearing gloves when using any cleaning solution.