I set out to find my own way to make some and I had a few duds before coming across this one. I tweaked it a tiny bit to fit what I was looking for and this makes a great little cube for washing!
1 Cup Borax
1 Cup Washing Soda
1/4 Cup Epsom Salt
First I started by mixing all the powders together. I made sure they get mixed up good because I wanted it evenly spread through all the cubes I'm going to be making. If you're not sure about the Borax, just eliminate that from the recipe, it won't harm it at all.
The lemon juice will foam when it hits the powder. I mixed it all in and got it a little sticky. When I was finished with that, I started to add it to the ice cube trays. I put in a little and patted it down, then when I ran out I did another cup to mix with the lemon juice.