I got this off of one of the frugal living sites and it works brilliantly for me so I thought that I would share it here.
1/2 a bar of grated soap
1/2 cup soda crystals (you find them in the laundry aisle of the supermarket)
1/2 cup borax
2.5 litres of water.
Grate the soap and put in a pan with the water. Heat until the soap has dissolved and add the borax and the soda. Stir until all dissolved. Remove from the heat and add 10 cups of water.
When it is cool add a few drops of your favourite essential oil. I use Eucalyptus oil.
I use half a cup of this in my wash and fill my fabric softener section in the machine with white vinegar.
You can also double the amounts of soda and borax if you have really dirty washes to deal with.