We highly recommend using a composting toilet when you can't properly remove the waste-water or "black water" from the tiny house. In situations where a septic tank or city/county sewer aren't an option, a composting toilet is the best way to keep the smell out.
The waterless design requires no water for flushing. There is no odor, due to the separation of liquid and solid wastes. A ventilation hose is vented outside and one 12 volt power hook-up for a small computer type fan is built directly into the unit.
So what breaks down the waste? The most commonly used material is sphagnum peat moss (organic) which is available at most garden or home improvement stores. It is usually available in a shrink-wrapped 3 ft cubic bale for $8 to $10. This quantity of sphagnum peat moss should sustain use of the head for a year or longer. The sphagnum peat moss should be organic, no additives.
Installing a composting toilet into a tiny house, though more expensive than a regular flush toilet, can be a great option when you don't have the waste-water plumbing option.