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TSP - TriSodium Phosphate. Available at most hardware stores. Used as a wall degreaser before painting, etc. Comes as a powder ou add to water. No fumes. Wear gloves. Read cautoins. Little old ladies have been using this for degreasing for decades.
What he said, but do a second washing with clear hot water, and change often. Get all that residue off. Then prime, and paint. I do this all the time. I buy older houses, renovate them, and sell them. I have done that a bit, well just for 35 years! I ain't house Bob, but I know what I know.