I always, always use the food processor to grate the soap, and make the dry version, 1 - 14.1 oz Bar Fels Naptha, 3 Cups Borax, and 3 Cups WASHING (not baking) soda. Been using this for a very long time now, and since I have such good results, I've passed the "recipe" to all of my friends. Now we ALL use this recipe and have cleaner clothes and save $$$.
I also use 1/4 cup of vinegar as a fabric softener, in the washer fabric softener dispenser and a ball of aluminum foil to stop the static cling in the the dryer.
All of the above work great.