Where can you buy trisodium phosphate?

Answer 1

Most hardware stores sell it. It is usually located in the paint department. Where I live it comes in a box that looks like a small milk carton. It's blue and kind of a teal colored box with T.S.P. in big letters.

----

Be aware that actual TSP is hard to find. Hardware and paint stores stock a substitute product whose labeling tries to hide the substitution. You will see a very large TSP with a tiny asterisk and somewhere else on the box is the word Substitute. The reason for this is, aside from TSP's excellent cleaning properties, the phosphate component makes an excellent plant fertilizer. So much TSP was getting dumped into the environment, causing lakes and ponds to get clogged with algae and other plant life, that a general ban on the use of TSP as a cleaning product was issued.

Unfortunately, the TSP substitutes require health warnings as they are not as benign to humans as the original TSP was.