Fungi do not excrete anything other than water. Fungi use almost everything they adsorb to build cells and chemically power their cells. There are other microscopic life forms that further break down what the fungi can not.
Fungi are particularly useful to humans due to the waste products they make during respiration. Waste is excreted via the hyphae. Like bacterial waste, the waste produced by fungi can be harmful or helpful. So it works both ways
