Marine sanitation systems and supplies
The Head (Marine Toilet)
Manual
pump heads are just what the name implies: you pump water in and
out of the bowl manually. They are designed to use "raw"
(sea, lake or river) water for flushing. The amount of flush water
can be controlled to some extent by how much you pump. The best
known are manufactured by Blakes & Taylors and Microphor Inc.
It's possible to add an electric motor (typically 12v DC current)
to some models; the motor simply replaces your arm in activating
the pump.
Electric macerating heads are only a little more complex than
a manual head. They are typically designed to use raw water. An
impeller pump replaces the piston type found in manual heads,
and there is also a discharge pump. Between the two is a device
called a macerator that is not totally unlike a blender or a garbage
disposal, it purees solid waste & paper. Like a garbage disposal,
a macerating head needs a lot of water, typically 1 to 3 gallons
each time it's flushed, or it will burn out.
Sanitation Hose
Sanitation hose has long been the subject of a whole lot of debate.
Some experts insist that anything less than double walled hose
is unacceptable, some even recommend the use of rigid PVC. In
fact, the first is an unnecessary expense, the second could be
the worst thing you could do.
There have been problems with hose in the past, and there is
hose on the market today that is totally unsuitable for sewage,
and it's impossible to determine, just by looking, whether a particular
white flexible PVC hose is suitable for use in sanitation systems
or not. Tek-Tanks can supply a sanitation grade hose. See Catalogue
for details.
If possible, run your hose without any low spots where sewage
can stand, and always be sure to flush the head sufficiently to
push all the sewage out of the hose and rinse behind it. As part
of the routine of closing up the boat, close the intake seacock,
flush the head dry, then pour about a 2 pints of fresh water into
the head and flush that through the system completely. If limited
holding capacity makes extra flushing each time the head is used
impractical, following this will solve most odour problems.
The standard for sanitation hose is flexible smooth-walled PVC,
1½" (except for the discharge from a macerator to
an overboard through-hull installed below the waterline, for which
the standard is 1"). Since the standard fittings on holding
tanks are 1½", when coming off a macerator to a holding
tank, it will be necessary to break the hose, using a 1"
to 1½" adapter. The standard for the hose from a holding
tank to the deck fitting is also 1 ½"I.D.
A range of pipe adaptors are available to suit sanitation hose
from the Catalogue.
Pump Out Deck Fitting
The
British standard (BS 7162) for the deck fitting is 1½" ID. The male hose barbs are all 1½". The deck
fitting should not have a chain linking the cap, (you can't connect
a pumpout with a chain in the way), and should be clearly marked
'Waste." Although the best quality deck plates are cast stainless
steel with stainless steel caps. Colour coded plastic caps, blue
for water, red for fuel and black for sewage are quite suitable
and are far less likely to mistake one deck plate for another.
Holding Tanks
As with all bandwagons, everyone who thinks he
can make a buck off it, wants to jump on. Consequently, just about
anything that will, ever has, or might hold liquid is being offered
for sale as a holding tank. It's an area of the boat where no
one wants to spend money, in fact that's true of the whole sanitation
system.
Although you'll see aluminium and stainless holding tanks, no
metal of any kind should ever used to hold sewage. Urine is
the most corrosive material that is possible to put next to any
metal. If you are in doubt (ladies will have to take our word
for it), notice the dividers between urinal stalls in men's toilets.
If that facility has been open for more than a week, no matter
how clean and well-maintained it is, even though the dividers
are stainless steel coated with enamel, you'll see rust stains
from the bolts that attach the dividers to the tile.
While the walls of a metal holding tank may last forever, the
welds will typically begin to leak at a seam or a fitting in two
to five years, and the tank will have to come out for repairs.
Sailing boats especially are often fitted with flexible tanks
also known as bladders. Bladders are invariably stuffed down any
opening large enough to take it, and only rarely are the bladders
secured in place. Since sailing boats are typically so much more
'active" than houseboats or cruisers, heeling side to side,
bladders move and chafe till they leak. Because the tank is in
an inaccessible place, it is almost impossible to install the
fittings correctly, and the tank is never checked or maintained.
Some aren't even vented, and it isn't at all uncommon for a bladder
to blow out its fittings. Furthermore it is all but impossible
to control odour in a flexible tank. The very qualities that make
bladders attractive to install, make them undesirable for
use.
Rigid polypropylene tanks as made by Tek-Tanks have sufficient
wall thickness to prevent odour escaping through the wall. If
the wall thickness doesn't continue to increase with size, the
tank walls will be too weak to support the eight pounds per gallon
that sewage weighs (meaning a 40-gallon tank must support 320
pounds); it will bulge and, at the very least, create leaks at
the fittings if it doesn't actually crack. There are polyethylene
tanks being sold as holding tanks through most of the marine catalogues
which have walls as thin as 1/8". These are just not suitable.
(All Tek-Tanks holding tanks have a wall thickness of 9mm
- 3/8") 
Holding tank systems
Notes, hints and tips.
1. Holding tank vent pipe should be 1½" (38mm) ID. This
will avoid blockage and possible implosion at pump out. It will
also allow air to circulate within the tank thus helping with
the natural biodegrading. (See section on Odour Control.)
2. When the outlet of the tank is in the side, drop hose below
the bottom of the tank to enable complete emptying of contents.
3. Avoid pipe droops. Support with suitable clips or bulkheads.
4. Chamfer inside of fittings to allow a smooth run.
5. Avoid tight bends which can cause resistance and blockages
in the pipe and minimise the number of bends.
Installation
When installing a system all connections should be double-clamped,
only materials specified for marine sanitation should be used,
and any below the waterline intake lines should include a seacock
that is easily accessible by the boat owner. There are one or
two heads on the market which require pressurised water and call
for tapping into the on-board potable water supply. Allowing the
sewage system to have any contact with potable water presents
an unacceptable health hazard. The manufacturers assure us that
check valves prevent any contact, but check valves can and do
fail. Therefore we recommend that all systems either utilize raw
water and a separate pump to pressurize it if necessary, or a
separate on-board water tank to supply the head. Vented loops
should be installed in all hoses to prevent backflow; if any part
of the system is below the waterline vented loops must be installed.
Odour Control
It really is possible to have a completely odour free
system! .................honest !
You may have read or heard, that the key to odour control is
the hose, that hose permeates with sewage and causes the system
to smell which leads to the kind of advice about hose we mentioned
above. That's a half-truth. The key to odour control is in the
installation of the entire system. What very few people in the
marine industry have learned is the very nature of sewage itself
and how it breaks down. Once you understand it and it's so simple,
you can do the same thing.
First of all, a marine holding tank must be exactly the opposite
of a septic tank. Holding tanks stink when they become "septic
tanks." Why does a septic tank stink? Because it is in an
airless environment. So what keeps a holding tank from becoming
a 'septic tank'? A sufficient supply of fresh air, in and out
of the tank.
Sewage contains two type of bacteria: aerobic bacteria (which
need oxygen), and anaerobic bacteria which thrive in an airless
environment; in fact anaerobic bacteria can't survive in an aerobic
environment, why is that important? Because it's the anaerobic
bacteria in sewage which produce the foul-smelling gasses; the
aerobic bacteria break sewage down, but do not generate odour.
So as long as there is a sufficient supply of air to the tank,
the aerobic bacteria thrive and overpower the anaerobic bacteria,
and the system remains odor free.
Enzymes do little if anything. Chemical products only mask one
odour with another odour, they kill anaerobic and beneficial aerobic
bacteria, and therefore create more problems than they solve.
Chemicals, unlike bio-active products, are also unwelcome in landside
sewage treatment facilities.
The anaerobic bacteria in sewage produce a variety of sulfur
monoxides and dioxides (which are the malodorous gasses), methane,
which has no odour but is flammable, and carbon dioxide which
also has no odor but creates the environment in which the aerobic
bacteria cannot live, but the anaerobic bacteria thrive. Carbon
dioxide does not rise or fall, it is ambient, like the atmosphere.
Without a sufficient flow of fresh air through the tank to allow
it to dissipate, it simply lies like a blanket on top of any pool
of sewage (whether inside a hose or a holding tank), suffocating
the aerobic bacteria and creating the perfect environment for
the anaerobic bacteria to take over. The system becomes "septic,"
and the result is a smelly boat.
To prevent this, let's start with the head: If at all possible,
the discharge hose, no matter whether it goes overboard, or to
a holding tank, should be installed, if at all possible, with
no sags or low places where sewage can stand. When a marine head
is not flushed sufficiently to clear the hose of sewage, that
sewage sits in low spots in the hose. Bits of it cling to the
walls of the hose. With no fresh air present the anaerobic bacteria
thrive and create their stinking gasses. If sewage stands in a
low spot, which gets no air, the smell will eventually permeate
the hose. This is what has given rise to the myth that the "wrong"
hose causes odour. Therefore, as we have already said, flush your
head thoroughly enough to clear the entire hose of sewage and
rinse behind it. And when you leave your boat to go home, flush
the head thoroughly one last time, this time with fresh water.
Until holding tanks came along, the hose was the source - but not the real cause of most odour.
Venting
In the holding tank, the key to odour control is the vent line; it must allow a free exchange of fresh air for the carbon dioxide
generated by the sewage. Therefore, those bladder tanks which
have no vent are all but guaranteed to stink; there's no source
of air into them at all. Boat builders, boat owners and boat yard
personnel who install holding tanks have always viewed the vent
line only as a source of enough air to allow the tank to be pumped
out without collapsing and an exhaust for methane (Many even believe
methane to be the source of odour.) Some take the attitude that
tanks are going to stink so the thing to do is run that vent line
as far from people areas: cockpits, sun decks, etc. as possible,
or make the line as small as possible. All of the above actually
create the very problem you want to solve.
Vent the tank with as short, straight, and level a line as is
possible, with no sags, no arches, and no bends. The minimum I.D
of the hose should be 1". Ideally, it should be no more than
5' long. If it has to be substantially longer, or if running the
vent line uphill can't be avoided, or if it's impossible to run
a vent line that does not go around a corner, increase the size
of the vent line to 1½". (In fact, when possible we put 1½"
vent lines on all installations. The British Standard MAS 101
actually specifies an 1½" breather or a multiple of breathers
meeting the same cross sectional area as an 1½".) If, for
instance on a sailing boat, the line must go up to the deck, install
a second vent line in order to create cross ventilation, or install
some means of forcing air down into the tank. We prefer to put
holding tanks in the bow of sailboats, under the v-berth, because
the hull just behind the point of the bow is the only place on
the hull except the transom that will never be under water when
the boat is on heel; it's the perfect place to install a vent
line skin-fitting.
The vent fitting should not be the same type as a fuel vent fitting,
a cap with a slit in it, but should be a straight open type.
A
vent filter may also be installed between the deck skin-fitting
and the tank. Use an inline filter if problems persist or you
have inherited an installation that may have not been correctly
installed in the first place. The MICROVENT activated carbon filter from Lee Sanitation is designed for use
with 1½" pipes and thus ensures a good flow of fresh air.
