Dirty feet show where you have been, so dream books read them as the marks a hard stretch of the road has left. Washing them is the old image of leaving that behind.
When this appeared in your dream, what were you feeling?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.