Porous and soft, a sponge may symbolically represent spongy exterior boundaries. It may comment that you too easily absorb the energy of others. As in “sponging of£ someone,” it may mention that you could be using people or are too dependent.... Ariadne's Book of Dream
Dreams of a sponge signify that you are receptive, allowing, and suggestible to the energy that is around you. You might be coming to terms with how you feel about others sponging off of you. Or your dream might be showing you where you must become more -reliant and considerate of the boundaries set by others. Also, this dream reflects your resilience, in that your life circumstances can squeeze you dry, but that you quickly expand back to your natural way of being. Consider the feeling tone of this dream. See Drink.... Strangest Dream Explanations
If you washed with the sponge, you will get credit for doing a good job at something.
If you squeezed water out of it, you will get money. But if you tried to squeeze the sponge and found it dry, you are being warned against taking any kind of risks with your money.... My Dream Interpretation