(one) hand washes (the) other

Translations
рука руку моет
I help you, you help me. One hand washes the other.
Я помогаю тебе, ты помогаешь мне. Рука руку моет.
Definitions
This phrase means that people help each other out with the expectation of mutual benefit; one good deed is returned with another. It emphasizes cooperation and reciprocity, similar to the idea of 'you scratch my back, I'll scratch yours.'