What I think about is, what am I putting down the drain and ultimately into the river/water-table? I want it to be as biodegradable and non-poisonous as possible. Liquid soap made of plant oils (such as Dr Bronners) seems like a good solution.
They would rot in the bottle if there weren't some preservatives in there. After the soap gets diluted into water, the preservative isn't going to work anymore.
