I wonder why TSP is in the paint dept?
I think it's meant to be used for cleaning paint off concrete floors, etc. I got mine at Lowe's.
If you have a paint brush that is rock solid with paint, you can put it in a container of very hot TSP/water solution and it will soften the paint and let you scrape a lot of it off. Several treatments can rescue a good brush.
It’s also good for washing stuff before you paint, but you have to make sure you wipe off any scum left behind.