This is my favorite DIY project of all time. I have jarred it up and gave it away for Christmas, I have made it several times, and it saves tons of money. Plus, making it makes your house smell amazing.
I have read that this works well with HE washing machines.
My recipe comes from my friends blog, but the following are from my own experience making it:
5 Gallon Bucket (you will fill this all the way)
Several Large Pots
1/2 Cup Borax
1 Cup Arm & Hammer Super Laundry Booster or Laundry Soda
A Bar of Laundry Soap
15-20 Drops Essential Oil (Optional)
Tea Kettle or similar sized pot for boiling water
Start pots of water (including a tea kettle) boiling, leaving one burner open for your saucepan.
Grate soap and put in saucepan.
Add just enough water to cover and heat on low, stirring enough so that it does not stick, until melted completely.
Add the teakettle of water to your bucket and melted soap. Stir until combined.
Add washing soda and borax (and oil) at this point. Stir until dissolved.
Add more boiling water until bucket is 2/3 full (I have only a couple of small pots and usually at this point I am adding hot water from the faucet to get the bucket 2/3 full and it still works great). Keep stirring. Then fill the rest of the bucket with hot (not boiling) water. Let stand.
After a few hours you should have the consistency of gelatin with some liquid around it. At this point you can keep it in your bucket or transfer some to a smaller jar to use in your washing machine. It only take 1/4 cup for a load. When I have a large load I use a heaping 1/4 cup.