The phosphate in TSP forms phosphoric acid, which is good if you’re cleaning out a fuel tank, to a point. I’ve heard of people failing to rinse TSP from their aluminum window screens (TSP is a common detergent used when cleaning siding), and finding the phosphoric acid had corroded them pretty badly. Be sure to rinse thoroughly.
I know what you mean about the fake stuff being forced on us by the eco-weenies and others. I keep my eye on the real TSP. If I start to see it go away, I’ll have to stockpile it. Already doing that with other things, like clear incandescent bulbs. If I could afford to bury my own fuel tank in the back yard, I’d consider buying a tanker of unmolested gasoline, but I don’t think my neighborhood association would allow it.