I bring along a couple plastic tubs and do my washing on the picnic bench.  I've only been to a couple places that do have washing stations.

Joecamper has a great one. I think there is a picture posted somewhere on the site if nit just PM him and ask him to post it.

Great idea using bus buckets, although I might not cut an opening myself, just to keep a dual use. I suppose I could do it, and install clips to pop the top back on.