I brewed last Sunday. My custom is to clean the brew rig the next day, but I got called in to work, and what with one thing and another I didn't get around to it until Wednesday. By then I had some God awful stuff growing in the remaining water! This isn't the first time that's happened, and I have been thinking of using it to make a sour, but this time something clicked. Sourdough starter!
I added 3 oz of water and 1 oz of the nasty runoff to 4 oz of flour and mixed it up. 24 hours later I had activity, so I fed it 4+4. Today I fed it 4+4 again, and the thing is going crazy! I'm going to feed it again tomorrow and then bake something Monday. I'll report back then, but it looks promising!