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Plumbing & Ventilation
especially at an angle, puts stress on the seat hinges and can dump the oc-
cupant at the most inopportune and embarrassing time!
A lot of people scoff at electric heads as extravagant energy wasters. But because
the electric pumps run so briefly with each flush, the total current consumption is ac-
tually quite low. The Jabsco Quiet-Flush Electric Head, for example, draws 10A, but
with a 30-second flush cycle, total energy used per flush is just 0.15Ah. Advantages
of electric heads include easier operation for inexperienced guests, and less chance
of clogging because the built-in macerator evacuation pumps grind up waste and
toilet paper before sending it to the holding tank.
Selecting the other components of the system
Seacocks and Thru-hulls:
Most head systems use a 3/4" intake seacock and
thru-hull for seawater flushing, and a 1 1/2" seacock and thru-hull for overboard
discharge. Bronze fittings are most common because of their strength and dura-
bility, followed by Marelon fittings for their nonconductive, noncorroding nature
(Marelon fittings are often used on metal boats).
All types of sanitation hose will eventually fail (smell) if sewage is allowed to
stand for extended periods of time. We recommend only smooth interior wall hose
because corrugated types trap waste and restrict flow. Rigid PVC does not pass
odors but is more difficult to route and does not connect directly to pumps and
thru-hulls. Still, it's possible to plumb part of the system with rigid PVC, switching to
hose where necessary. The best hose for containing odors is SeaLand OdorSafe
Plus, followed by Shields Heavy Duty Vinyl Hose (#148) or Super Head Hose (#101).
Reduce odor by:
Heating hose to fit over barbed adapters can dangerously weaken the hose;
instead buy fittings specifically made for 1 1/2" sanitation hose.
Seawater vs Freshwater Flush:
Okay, using your limited supply of fresh water
to flush the head seems a ridiculous waste, but electric heads from Jabsco and
SeaLand use very little water-some models as little as a pint or two. And freshwater
flushes greatly reduce bad odors in the system caused by all sorts of microorgan-
isms dying and decaying in the bowl-plankton, krill, you'd be surprised!
A common cause of boat sinkings is from backflow created by
siphons in the head and engine seawater intake hoses, and head discharge
hose. Vented loops installed in the hose above the waterline prevent siphons
from occurring and don't impede normal flow. They're usually mounted against
a bulkhead. We sell both bronze and Marelon models.
Thick-walled (1/4" or thicker) high-density polyethylene tanks
are the most sensible choice. They are light, won't corrode and are much less
expensive than metal or fiberglass tanks. While thinner wall tanks rarely burst,
they can bulge so much that fittings are stressed to the point of leaking. Your
nose will alert you, but it's safer to buy a quality tank in the first place. We sell
Todd and SeaLand tanks in various wall thickness. Taller, narrower tanks can
be emptied more completely but are more difficult to secure. Plumbing attach-
ments should be as low and as high on the tank as possible. Flexible tanks can
be used when spaces are oddly shaped or inaccessible but they lack the odor
resistance and strength of rigid tanks so we don't recommend them for waste.
We feel the best Y- or diverter valve is made by Whale, in part be-
cause it has a center position that closes both ports. Other brands, however,
may integrate into your plumbing more conveniently depending on the direction
your hose runs. The Bosworth Y-valve can be surface-mounted so that you don't
have to climb into a tiny locker to change directions. Forespar's Marelon valves
are very strong, and Jabsco valves can be adjusted to a variety of configura-
tions and are lockable for USCG inspections.
Discharge pumps are used to empty the holding tank overboard. We
recommend large diameter diaphragm pumps because they are the least likely
to clog. The Whale Manual Waste Pump is the best choice among non-electric
pumps. Unlike aluminum-body pumps, its plastic body won't corrode. Macerator
pumps, such as those by Jabsco and SHURflo, grind waste for easier passage
through the sanitation system. When used as discharge pumps (from holding
tank overboard) be very careful to monitor the tank level because they can burn
out pretty quickly if run dry. A more durable solution for pumping holding tanks is
the SeaLand Sanipump diaphragm pump, which can be run dry without damage,
or the Whale Gulper pulverizer toilet pump, which can handle solids up to 1 1/2".
Be sure your seacock is open before trying to pump out the tank. When an
electric pump tries to pump against a closed outlet its valves can sometimes
ing as anything you can imagine (yes, the author had to do this one time at Santa
Cruz Island in Southern California, and wishes he hadn't.) And even if the pump
isn't damaged, you could cause a rupture in the system-yech.
Tank level indicators reduce the risk of overfilling the holding
tank, which can push sewage out the vent line, or, if that line is clogged, rupture
the system elsewhere. Mount monitors near the discharge pump switch so you
can empty the tank as soon as you determine the tank is nearly full.
Deodorizing the holding tank
Any discussion of holding tank odor generally involves a discussion of aerobic
and anaerobic bacteria, which is better and which smells worse. Many experts
recommend promoting aerobic bacteria growth by purposely injecting air into
the holding tank, causing waste-consuming bacteria to thrive, while at the same
time reducing the anaerobic bacteria, as they are one of the sources of odor.
This requires some sort of air pump and a free flowing vent in the tank (vents
are notorious for becoming clogged with everything from toilet tissue to spiders).
Groco has taken this idea and come up with SweetTank
, a small (3 watt) pump
that injects air into the bottom of your holding tank. The result is a dramatically
lower odor level, even in sanitation systems that have traditionally been odor-
prone. Of course, SweetTank isn't a solution for sewage spills or porous hoses,
but it will make the contents of your holding tank easier to coexist with.
The other approach is to use a holding tank product that consists of bioactive
aerobic bacteria-sort of priming the old bacterial pump. While this approach is
at least theoretically sound, in our experience, the bacteria require more time to
work than is often practical or desirable. When harbor-hopping, for instance, you
may well be pumping out your holding tank every day, which doesn't allow time
for these microscopic critters to do their jobs. And in the meantime, malodors
may well escape from the ventilated tank. For more information see the West
Perhaps the best solution is a combination of injected air and biological treatments.
We're encouraged by this approach since it uses natural processes to control odors,
and should the resulting contents be pumped overboard when legal, the boater
hasn't loaded a bunch of chemicals into the mix to control odors.
Regardless of how much boaters really contribute to water pollution, the ines-
capable truth is we need to do our part, at least as a symbolic gesture. Creat-
ing a good, odor-free sanitation system isn't that hard. Start with an intelligent
design, buy quality components, and maintain them. With the ability to pump out
ashore and discharge legally offshore you assure yourself of not having to cart
around waste longer than necessary. After all, there's more where that came
Selecting a Sanitation System
Below-waterline installation requires vented loops to prevent
back-siphoning (and potential sinking) when the boat heels
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