Sawdust will be a key component in tomorrow’s toilets. It is part of the basic kit that makes up a composting toilet, at least those created by S’Klo, a company from the Black Forest in Germany. Most other firms in the business use a similar model. Fridolin Einwald and Michael Heizmann build the toilets themselves and deliver them when clients order them for use at a wedding, say, or a company party or to be dotted along a hiking trail. According to Einwald, many of their clients are “nature-oriented and environmentally aware.” The thinking with this kind of toilet is to save water by using sa…