Trisodium Phosphate. It can be purchased at the local home improvement box stores.
Getting harder to find as states and jurisdictions ban or cap phosphates in detergents at .5%, TSP is no longer at big boxes in Michigan.
It’s a product that no one will ever check your car for driving across state lines. It’s one of those products that you buy when you’re in another state if it’s unavailable in your own.
