It is probably wise to avoid using this product. Reading through the information about the tablet, it releases chlorine into the flush water. The chlorine kills the critters that die and stink but can also harm the soft plastics in the system. The chorine probably forms and acid which dissolves the calcium build ups. It may be worth something for boats that only discharge overboard, but for holding tanks the chlorine may kill off the the good bacteria which helps to reduce holding tank odors.