The major objections to installing holding tanks, yards of piping, myriad fittings, cantankerous discharge systems malodorous fumes, can be ameliorated with modern materials and clever installations. The K.I.S.S. Type III, no-discharge holding tank system with overboard capability where legal, is the most advanced of those clever systems. The KISS system allows you to install or retrofit the best possible working system without complicated plumbing, electrical connections and drilling a minimum number of holes in the boat. The concept The concept is simplicity itself. The tank, installed above the waterline, is emptied overboard by gravity.
All waste goes through the tank.
The toilet pumps directly to the top of the tank. The toilet itself can be either manual or electric, it makes no difference. One of the fittings goes to the seacock, the other to the deck pump-out fitting. To use the tank, you close the seacock. To flush straight through, you open the seacock.