As my step-son likes to say; I am a vault of little known and/or useless knowledge!
Kona has just done the pre-washing for you, so all you have to do is get it wet and you are ready to rock & roll! I learned about the pre-wash from my sister, the art teacher. She was doing a project at school and had a bunch of leftover dye. She told us the stuff to get to wash the fabric in. It's called Synthrapol SP textile detergent.

As I am sitting here reading the label, it says it removes unseen grease, oils, & silk gum from cotton & silk. After dyeing, if you use it in the wash water, it keeps the excess dye in suspension, preventing "back-staining" on lighter fabrics. It also has some nasty waring stuff on the side, so I wouldn't be drinking it, or anything like that.
This came from Dharma Trading Co. http://dharmatrading.com/ . This does not look like a website you really want to poke around on. This hobby looks like it could be as dangerous as quilting, AND you could use the excuse that you will use the dyed fabric in quilts. BAD, BAD, BAD.
C