Here is a recipe we’ve been using for our dishwasher soap. Very simple and works like a charm. (Make sure you label adequately.)
1 cup of Borax
1 cup of Arm and Hammer Washing Soda
1/2 cup of Kosher salt
1/2 cup of citric acid
Mix all ingredients together and store in a plastic or glass container. We store ours in one of those olive bar containers you get at the grocery store. We use the medicine cups that come with liquid medicine as our measuring device. We put about 3/4 of that little cup into our dishwasher soap dispenser for each load. We also used vinegar in the rinse agent dispenser.
We have found that sometimes the boxes of Borax and washing soda on the grocery shelves are full of lumps, so we use a sifter to break down those lumps and have a uniform mixture for our dishwasher soap. The salt will not go through the sifter we use, but everything else breaks down quite nicely.
We have also learned through use that this mix tends to clump due to the citric acid. It still works, just be aware that it will clump up.
UPDATE: We have actually stopped using this recipe and are back to buying dishwasher detergent. This recipe worked great for about 3 weeks and then our dishes started having a bad film on them. We made sure there was vinegar in the rinse agent, but our dishes were still not coming out clean. Plus, the clumping became one large clump and was almost impossible to get out of the container. We had to use a knife to break up the mixture. We’ll let you know if we come up with something better.