Wether for washing your hands or dishes, whatever you use will inevitably penetrate the soil and ground water supply. We therefore want to use biodegradable soap (alternatives) only.
One cleanser most readily available but often overlooked is ash.
You can simply keep it in a bowl next to the sink replacing non-degradable soaps.
Instead of buying regular soap we can choose to just buy it's active AND biodegradable ingredient which is SLS. SLS is what makes (not only soap but most cosmetic products) foam, lifting away dirt and oils.
It's derived from from petroleum or natural sources (e.g. coconut- or palm oil).