A couple recipes for you!
1 cup baking soda
4 cups vinegar
4 cups warm water
Baking soda and vinegar react, of course, so you need to mix the vinegar in very slowly. Stir it well and add half a cup to your rinse cycle. This does not get clothes as soft as commercial softener, but personally, I don't like the way that feels, anyway (it feels...gunky!)
Onto sourdough. It's easily one of my favorite breads. There are a number of ways to do starter, but I do the plain old way- 1 cup of flour (I normally use whole wheat) and 1 cup of warm water. Cover it with a light cloth and let it sit in a draft free spot for a few days (I prefer near the stove so it gets some warmth), stir it once a day. What you're doing is trying to "catch" wild yeast, so there's no guarantee it will work. It should have a sour, alcoholic smell and some bubbling. It should not smell rancid. If you can't catch yeast that way, you do 1 cup warm water, 1 packet, yeast, and 1 cup flour.
Because I'm the only one in the house that likes sourdough, I don't bother to keep my starter fed. I put it in a mason jar that has a couple holes poked in the lid and keep it in the fridge. To revive, stir it up, add 1 cup warm water, 1/2 cup flour, and 1 tsp sugar. Cover and let it stand in a warm spot until foams.
Most sourdough recipes start with a sponge. So now you have your starter, put 1 cup of it into a large bowl with 2 cups of warm water and 2 1/2 cups of flour. Mix it, cover, and let it rest for a few hours.
If you have surplus sponge, you can use it to feed your starter! Just replace whatever you took out, or pour off some of the starter and add an equal amount of sponge.