Among the nicest features of a larger boat is having two heads. That way, when one breaks, as they inevitably do, you need not repair it immediately. A marine head usually consists of the bowl and its pump, a holding tank vented outside the boat, inlet and discharge seacocks, and a pump-out fitting, all connected by various kinds of hose. Seawater is pumped from the inlet into the bowl. This water and anything else in the bowl is pumped either to the discharge outlet or to the holding tank. A y-valve determines which, and the USCG requires this y-valve to be locked in the holding tank position when not offshore.
Holding
tank
The holding tank can be emptied via a deck fitting at a pump-out station or its contents can be macerated and pumped through the discharge outlet where it is legal to do so. In coastal boats that never go offshore, the head can connect directly to the holding tank, eliminating much hose in the outlet loop as well as the discharge thru-hull, with the understanding that the head will not be operable once the holding tank is full unless there is some acceptable means of emptying it, such as a specialized hand pump applied to the cleanout port on the deck. Hoses
The intake line should have an anti-siphon loop that rises well above water level to prevent water from siphoning in and perhaps sinking the boat if debris lodges in the valves and prevents them from closing. It will also benefit from a strainer to trap organic matter before it can lodge inside the flushing chambers beneath the rim of the bowl; however, this strainer might do more harm than good unless you clean it regularly. The discharge line also needs an anti-siphon loop, even if it connects directly to the holding tank, because otherwise the boat can sink, and in a most unpleasant way, if the discharge thru-hull is left open. Except for the intake hose, which carries only sea water, all other lines should consist of specialty sanitation hose. The most expensive sanitation hose is not necessarily the best.Blocked
head
If the head becomes blocked, put some hot water in the bowl and let it sit for a while, then gently try the pump again. Many sailors assert that nothing should be put down the head unless you have eaten it first. A little thin toilet paper does no harm, however. The thinnest grades at the supermarket are as good as the expensive marine toilet paper sold in boating stores. Heavier two-ply paper will likely block the pump. Consider using the hand shower as a substitute for paper if it has a long enough hose to reach the head. Use only the cold water, if you do this, because it is a nasty place to get scalded. Maintenance
Because it is flushed with sea water, a head and its lines might benefit from occasional cleaning to remove mineral deposits. Opinions vary. If performed monthly and in a place where it is legal, a quart of vinegar pumped slowly through the head and out the discharge seacock over a period of ten or more minutes can dissolve minerals and will probably do no harm.Treat the anti-siphon valve also by removing it and soaking it in the acidic solution. Never pump vinegar or anything else, except sewage, into the holding tank. If not performed monthly, this kind of cleaning is futile and instead a balky valve must be disassembled so that salt deposits can be chipped off. A better option might be simply to carry spares and replace the valves when they eventually stick.
Lubrication
Because it has rubber parts, a head might also benefit from occasional lubrication. Authorities are mixed on this topic, also. Special oils can be purchased, although mineral oil and even vegetable cooking oil probably work equally well (or equally poorly). Just pour a cup or so into the bowl and pump it out the discharge seacock, slowly and in a place where it is legal to do so. This lubes only the output side of the pump, of course, except for oil that the input side might pick up from the pump walls. You could remove the intake hose and pour oil into it, but that will get oil into the flushing chambers beneath the rim of the head where you do not want any. Never pump any oil of any kind, nor anything else except water and sewage, into the holding tank.Odor
Do not tolerate a bad smell. Verify first that the holding tank vent is not blocked. Insects like to nest in these vents, a filter in the vent line can become clogged, and sewage can enter the hose when the boat heels while the tank is full. Gasses forced out of the holding tank, when flushing the head, must escape into the boat if not out the vent. Ideally, the vent should admit air as well as discharge gasses, making inline filters a bad idea. To check the holding tank vent, remove its hose from the holding tank and, taking suitable precautions, blow through it.Check next for leaky connections at each end of each hose and all around the bowl. If the vent is not blocked and nothing leaks, rub a soft, clean cloth over every hose surface and fitting, including the sea water intake, stopping often to sniff the cloth. This will isolate a slow leak or a hose that is irreparably permeated with sewage.
When replacing a holding tank, get the thickest polyurethane tank available. A thin tank will flex and bulge and eventually might crack. Fasten the tank securely so that it will not shift when filled as the boat heels. If using straps, pad them with blocks of wood to protect the tank.
A bad smell results from anaerobic bacteria in sewage that sits where air cannot reach it. To avoid bad smells, simply prevent the sewage from sitting anyplace except in the holding tank and ensure that the holding tank is well ventilated with fresh air. Route all hoses without low points where liquid can collect. Flush the entire hose completely each time sewage passes through it. Use the shortest possible run of large diameter hose for the holding tank vent—3/4 in is not too big—and keep it free from blockage. Do not pour biocides or other liquids, such as bleach or cleaning products, into the head.
Rebuilding
a head
You can rebuild most heads using readily available parts kits. These sometimes cost a sizeable fraction of the price of a new head, so that simply replacing the head might be a better alternative. If you have just one head, and it clogs or breaks on a cruise, disassembly and repair might be the only option. A major part of almost every head is the weighted flapper valve, which always has the weight up and the largest side facing the direction of flow. Another is the duck-billed joker valve that always points in the direction of flow. If the pump uses leather cups, they will face in opposite directions with their flat sides together. Winterizing
a head
Besides when needing repair, heads are often removed for the winter, since the best way to winterize a head is by storing it in a warm place, whereas simply flushing antifreeze does not protect the seawater input side of the head. The only trick to removing a head for disassembly is remembering to close the intake sea cock. Replacing rubber parts annually is perhaps better than trying to lubricate them as described earlier. Before reassembling, clean and polish all surfaces, especially where there is a gasket or sealant. Do not over-tighten the nuts at the base of the head, lest you crack the bowl.Composting
toilet
An alternative to the marine head, especially on a cruising sailboat, is a composting toilet. The name is slightly misleading: Most marine units are really urine-diverting dry toilets. They separate liquids from solids, keep the solids relatively dry, and use ventilation and a drying medium to suppress odor and begin decomposition. The material does not stay aboard long enough for full composting. The bowl is designed so that pee goes forward into a separate container or drain, while poop falls into a solids chamber that contains coconut coir or peat moss. After use, you turn a crank or agitator to mix the solid material. A small 12-volt fan draws air through the solids chamber and exhausts it outside the boat. No water is added and nothing is pumped.
A conventional marine toilet system has a surprising amount of equipment: The toilet itself, intake and output seacocks, a pump, hoses, Y-valves, holding tank, macerator, and deck pump-out fitting. A composting toilet can eliminate almost that entire sewage system. The biggest advantage—no black-water holding tank—is perhaps the best argument for a composting toilet. Eliminating two below waterline hull penetrations also recommends them.
A separating toilet used by a small crew can go weeks between emptying the solids container. The liquid container fills much faster and needs attention every couple of days. This is the inconvenient part, especially in waters where it cannot legally go overboard. People sometimes say, “I only empty my composting toilet once a month,” and assume nothing else needs emptying. They are talking about the solids, not the liquids.
Emptying the solids is less unpleasant than it sounds. Because a constant flow of air has dried the material, it tends to resemble damp or even dry potting soil rather than sewage sludge. With some designs you can put a heavy trash bag over the solids container, invert it, and dispose of the bag as permitted locally. Then you add fresh dampened coir or peat. No special cleaning is needed, as some residual material is harmless and can help the process.
Marine-head odor most often comes from permeated sanitation hoses, stagnant seawater in the intake plumbing, holding-tank vents and plumbing leaks. A dry toilet has none of those and produces less cabin odor than a conventional marine head. The vent outlet usually doesn't emit a strong sewage smell either because the material is being kept aerobic and relatively dry. The liquids container might smell slightly of pee. Use a spray bottle of white vinegar to fix that, spraying it down after each use. This can be the same bottle used to fight mold and mildew.
Installation can be easier than replacing a marine head, needing only a secure mounting surface, 12-v power for the fan, and a 1.5- to 2-inch exhaust hose leading outside in a spot protected from wind and water. The toilet and its liquids container must both stay well secured when the boat heels or pitches in waves.
Crew cannot substitute the hand shower for toilet paper, as discussed earlier, because the bidet water would end up in the wrong place. Ordinary tissue can go into the solids container or else into a separate waste bin, which greatly increases the time between emptying.
One of the less-advertised drawbacks is that fruit flies or similar insects might colonize the solids chamber, particularly in warm climates. Keeping the mixture properly dry, with continuous ventilation, and keeping the toilet closed greatly reduces this problem. It matters more on a boat in Florida or the tropics than it would on a boat in Maine.
Three well-known brands are Nature's Head, Air Head and OGO. Which composts best is less important than physical dimensions, seat height, ease of removing the urine bottle, solids container removal clearance, positive latching, ventilation arrangement, and how securely everything remains in place while heeled. An easily overlooked measurement is vertical clearance. Some of these toilets are fairly tall. In a small sailboat head compartment, that can make sitting uncomfortable.
A conventional head is perhaps best on a weekend boat with lots of guests who might need instruction. For a cruising sailboat used mainly by a small crew, the separating and composting approach becomes much more compelling. An especially interesting possibility on a larger sailboat with two heads is to keep one conventional, for use offshore where it can be pumped overboard, and convert the other to a composting toilet.