I have been making my own liquid laundry detergent for awhile now. I started doing so when I was first divorced and BROKE. I still make it even though I can now afford to buy detergent in the store. It's FUN and VERY gratifying! (I also make my own vanilla extract, soap, body butter, and a few other things because I LIKE squeezing a penny until it BLEEDS! I also make these thing BETTER than what you can buy in the stores!)
When I make my detergent, I put the water and soap shreds in a large glass measuring cup and zap it in the microwave rather than cooking it on the stove. It's a LOT easier and FASTER! I use a stick blender to mix it (as I do with my soap) and after it turns to gel. (I mix the water back into the gel.) When I want to transfer it to an old laundry detergent bottle, I just put a few blobs back into the measuring cup and heat it again in the microwave. It will turn into a nice thick laundry detergent that you can pour into the container but will then gel back up so that you have to SHAKE the container before trying to use it.
BTW, I live in Texas. We'll do just about ANYTHING to keep from using the stove or oven in the summer!