This is how I use Farmers Reducer. I buy the Kodak product and mix it in two small bottles until I need it.
When I get a print that's too dark I slip the whole print into a tray of Reducer and lighten it up a bit. Now sometimes I get a print that the white is just too dark... like a cala lily on a black background. So what I do is, I take some cotton balls and apply the Reducer to the white area to lighten it up.
Of course this happens too slowly for me so I get frustrated and put the whole print in the tray. Then I leave it in the tray too long and totally bleach out the white areas, ruining the print.
Then I find the negative, reprint the photo lighter, and throw away the print that I over lightened.
I must enjoy using it this way since I've repeated this a number of times and have become very skilled at it.