"Pete C." wrote:

So I'm wondering if there is any additional info about just what
can and can't be used for a chemical cleaning product for up-
stream pickup in a power washer.

Spend the $20 on a downstream chemical injector and don't worry
about which chemicals to use.

A downstream setup is garbage (more lines, cumbersome, etc) and who
wants to do that when your pump has a soap pickup tube built-in?