and other chemicals can then cause corro-
sion. (That said, many of my aluminum boats
have integral aluminum holding tanks with
no problems.) Even the black water itself
(marine sewage or effluent is termed black
water) can potentially cause corrosion over
time. Top-quality 316L stainless steel holding
tanks are excellent if the proper weld filler
has been used and proper welding proce-
dures employed. (No other stainless alloy is
up to the job.) Such tanks will last a lifetime.
Monel is another excellent option. But stain-
less and Monel tanks are expensive (Monel
particularly so), heavy, and almost always a
custom order.
Plastic Tanks
The best remaining material is polyethylene.
It’s light and totally corrosion-proof. It is
plastic, however, and can suffer from some
odor permeation. The better quality and
thicker the poly tank, the less likely there
will be odor or leak problems. Once again,
SeaLand’s polyethylene holding tanks seem
about the best available (Figure 21-8). They
are fully^3 / 8 inch (9.5 mm) thick, which is
thicker than most others, and so virtually
odor-free. Available in an array of shapes,
they range from 9 to 52 gallons (34 to 200 L).
Remember, though, that whatever tank you
install, you can reduce odor and any corro-
sion by being sure to completely flush the en-
tire tank and sanitation system with fresh wa-
ter at the end of every season. Even the best
PVC hose and poly tanks will eventually ab-
sorb some effluent and thus transmit some
odor if you leave them year after year with
sewage sitting in them for months at a time.Types of Marine Toilets (Heads)
We’ve looked at my favorite marine toilet, but
there are many other fine choices. The most
common marine toilets are- bucket
- Porta Potti (toilet with self-contained
holding tank) - direct drop (gravity discharge)
- plunger pump with joker valve
- pump with macerator
- water-jet macerator
- manual diaphragm pump vacuum
- powered vacuum
The Cedar Bucket
The bucket is the oldest and simplest, but most
of us aren’t into that sort of roughing it. True
wooden cedar buckets are best. The cedar
greatly reduces odor. Of course, you must
empty the bucket after every use. The cedar
bucket should fit into a recess (often a hole
in a plank or ply panel) to ensure it doesn’t
slide around and should have a seat lid that
fits on top, so you can do what’s needed in
comfort.Porta Potti
The common term Porta Potti is actually a
trademarked name by the Thetford Corpora-
tion that’s often generically applied to most
self-contained, portable toilets with a built-
in holding tank and a freshwater flush tank
built into and surrounding the seat. The hold-
ing tank usually removes to empty at the
nearest land-based toilet. These toilets are
complete Type-3 sanitation systems and meet
all requirements for all waters.Direct-Drop or Gravity
Toilets
Direct-drop or gravity toilets are built-in toi-
lets. They must be located nearly vertically
above the holding tank. When the toilet isChapter 21:My Favorite Head
Figure 21-8. Plastic holding tanks
(Courtesy SeaLand)