The Pink Stuff
I mixed up my giant 5 gallon bucket last spring and it's still going strong! Remember that 5 gallons makes 10 gallons of detergent because you mix it with equal parts water before you use it. The best part the first batch (the most expensive) comes out to just over a penny per load! A penny! And the best part is since you only use a cup of borax and a half a cup of washing soda you have plenty left for several more buckets full. All you have to do is buy your $1 bar of soap. So that's $1 for 10 gallons of laundry detergent! You can't beat that.
Here's the recipe I used from the blog "Just a LIttle Nutty"
What I've Learned
First off remember to get a lid for your 5 gallon bucket. (They sell them at Home Depot) That's a must. Also if you have a food processor you may want to use that instead of the cheese grater it will go a lot faster. Another time saver is using a drill with a paint mixer attatchment. I bought one at Harbor Freight for $4. It makes the detergent a lot smoother and easier to pour. I keep my big orange bucket in the laundry room and just refill a half gallon bottle as needed. You're going to want to break out your drill and mixer before each refill just to mix it all up.