The same applies to washing stains in clothes.
If you are taking a shower or bath in your dream, this could indicate a problem that overshadows you in waking life.
If you are washing your hair, this is connected to your emotions, and if you are washing your genitals, there may be some kind of sexual adventure in waking life that you are ashamed of. You could also be worried about sexually transmitted diseases.
If you are cleaning your home, this could suggest that you want to get more organized in your waking life, but before you can do that you need to dispose of dirt or dust; this may refer to ways of thinking or responding that are clouding your judgments in waking life.
If you were watching a washing machine in your dream, this is a reference to your daily routine and the boredom you feel.
If you are trapped in the washing machine, you feel stifled by your daily routine; it will therefore be important to make changes in daily life as soon as possible.