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For some odd reason, whenever I talk to people about the house, the toilet is what really grabs their attention and elicits the most questions. Since the greywater system can't handle human waste, we installed a composting toilet. Composting is a process that breaks down various kinds of organic matter through aerobic or anaerobic microbial activity.
If you come to the house and go to the bathroom, you'll notice that the toilet looks similar to other toilets in that it has a seat and a lid (photo at left). But you won't find any water tank or handle for flushing, and when you open the lid, you won't see water. You'll see a 12" black polyethylene chute that's connected to a large composting tank (photo below right) that sits in the basement directly below the toilet. The house has two bathrooms, each of which has a toilet that has to be directly above the tank. Take a look at that picture on the left again. That galvanized, spiral duct is not part of the HVAC system; it hides the polyethylene chute for the second floor toilet.
The most common question I get is about the smell: "Won't that make your bathroom stink?" The answer is, no, the bathroom actually smells better than bathrooms with conventional toilets. The reason is negative pressure. There's a 5 Watt fan that runs continuously near the top of the toilet tank. It exhausts air from the tank through a 4" PVC pipe that is vented above the roof. So, any smells from the bathroom get sucked down into the toilet instead of lingering. The fan, by the way, is powered by the same 12 V DC batteries that power the booster pump in the basement. If the utility power is interrupted, our composting toilet fan keeps running.
There are many makes and models of composting toilets on the market. We chose the Phoenix R-200 by Advanced Composting Systems. In case it's not obvious from the picture above, the tank is large; it measures 40" x 61.5" x 68".