A couple tablespoons of baking soda
A few drops, or a small squirt, of Dawn dish soap.
Directions:
Fill your detergent cup with baking soda, you don't have to be precise, but with mine this ends up being a couple of heaping tablespoons. Then add a few drops of dish soap. I have a pump dispenser for my dish soap, so I just put about half a squirt in there. Close the cover, and run dishwasher as usual. That's all.
I experimented with quantity of dish soap. The first few recipes I read said just 2 drops, but that just didn't feel like enough to me, to really get a very full load clean. So I gradually added a little more until I felt comfortable. I haven't yet found an upper limit, but I haven't pushed it too far.
The baking soda is VERY important here. Don't try this without it! It keeps the soap from forming suds. The reason they tell you never to use liquid dish soap in your dishwasher is because of the suds - you'll have bubbles all over your floor. But the baking soda apparently prevents that, so it allows the soap to do the grease cutting and cleaning, without making all those bubbles. I've opened my dishwasher at various points in the cycles to see what's going on in there, and there are no bubbles. I'm not scientist, so I'm not going to try to figure out why any of this happens. All I know is, my dishes are getting clean and I don't have soap all over my floor and I didn't have to buy dishwasher detergent.
I have not tried this with other brands of dish soap. I've tried lots of other brands of liquid dish soap for hand washing, and I keep coming back to Dawn, so that is what I used for this. The more natural and/or less expensive brands just don't work as well. I found that I was having to use so much more soap to just wash a sink full of dishes, that it just wasn't worth it.
I pour my dish soap into a pump dispenser that I keep next to my sink. I like this one because the spout extends out far enough that you can just pump it right into the sink.
So that's it. Dish soap & baking soda! Let me know if you try it!