Millennium Dragon has two holding tanks, one in each bow, for the heads. Most of the plumbing is reasonably standard. Waste pumped from the heads is transported through large PVC pipes to holding tanks in the bows located below the floor of the self draining forward deck lockers. These pipes enter the top fill fitting of the holding tanks. One arm (upper, deck pipe) of the “T” fitting connected to the lower/drain aperture of the holding tanks connects to the deck waste fittings for pump out when near shore, USA. The other arm (lower, overboard discharge pipe) runs aft to a point under the lower (sink) cabinet in each head. A hole cut in the floor of this cabinet reveals a large PVC ball valve fitting. Aft of this fitting the pipe is connected to a large through hull fitting. Opening the valve allows overboard discharge of the holding tank where regulations allow. The valve handles have a 1/4” hole drilled so that a nylon wire tie may be used to secure the valve in the “closed” position. This tie must be cut if the valve is to be used where permitted. A new tie is fitted after the valve is again closed. So far standard stuff. The innovation is on the holding tank vent side. A vent that remains open is necessary or the holding tank becomes pressurized. Also, this vent pipe should have a water trap in it so that tank odor remains trapped in the tank. This was accomplished using 1/2” PVC pipe. The water trap is kept “watered” with mostly fresh water because the design of the deck hatch openings for the forward, self draining sail lockers. These hatches are flush fitting into a “gutter” molded into the deck. This gutter had no overboard discharge so that with rain or heavy sea spray, some water entered these self bailing sail lockers. Not generally a big problem aside from some dampness issues in the lockers but, after all, these are self bailing deck lockers and could not be expected to remain dry as a bone. The water in these gutters did, however, offer an opportunity to supply water to the water trap for the holding tank air, decompression lines. Rain and/or sea spray are then used to fill and flush the water traps. Excess water simply flushes the air vent and flows overboard. Pictures of this system may be viewed below.