Doing a simple conversion on my cargo trailer installing a small kitchen and toilet room. The tanks are above the floor under the cabinets, and the low profile toilet sits directly on top of the wastewater tank. There is no need for a third graywater tank since there is no shower. The fresh water tank is 13 gallons and the wastewater is 16 gallon. Just Needed to cut about a foot square hole in the floor for the low end and drain, and box in the black tank.