Use white vinegar, water, and a 5 gallon bucket drilled with 1/4″ holes and you’re good to go. Before use, it’s best to ensure they’re completely dry… some throw them into an oven for 400 degrees until dry. I don’t. I leave mine out because I clean them well in advance of needing them. I dry mine naturally.
Hydroponic mediums aren’t cheap. Clean and reuse your Hydroton expanded clay pellets and save some money. Cleaning is simple.