Along with my "PO-BOY" kitchen sink, I have a 3 gallon solar shower.
A few hours laying on a warm rock with even overcast skies, brings in warm enough for a shower on my lay-over/camp days.

Travel days, I can fill it enough to use to wash soapy dishes back in woods.
Like PJ, I find a hole to dump soapy water in.

I like unscented Dawn dish soap. It's concentrated so a little goes a long ways.
I figure if it's good enough for cleaning wild life covered in oil and disposals easily, it's good enough for back country use.