also won’t have water sloshing out in rough
seas. Most other toilets allow you to pump to
a dry bowl in one way or another. Be sure any
toilet you install has this feature.
The level of water remaining in the bowl
(during normal flushing with the lid closed) is
controlled by a vent-plug fitting on the intake
hose—an “air bleed valve,” or simply a hole
at the highest point in the seawater intake
hose (see [3] in Figure 21-2). If this hole is too
small, the vacuum won’t release soon
enough, and the bowl will be too full after
flushing. (Note that this forms the vented
loop for the Blakes Lavac.) Too large a hole,
and you won’t get enough vacuum and the
bowl won’t fill high enough.Blakes Lavac
Drawbacks
Nothing is perfect, and the Blakes Lavac is no
exception (though the drawbacks are slight).
One drawback is that it takes a good couple
of minutes for the vacuum to finish bleeding
out of the bowl after a flush. Until this hap-
pens, you can’t lift the lid to use the toilet
again. If you’re impatient and force the lid up,
you’ll likely pull the seal off the underside of
the lid. This doesn’t hurt the first dozen or so
times (you just reseat the seal), but ultimately
it can damage the seal.
Another minor drawback is appearance.
There’s nothing wrong with the look of the
Blakes Lavac toilet, but there’s nothing styl-
ish about it either. The head looks fine and
fits the decor of most ordinary cruising boats.
If, however, you have a large, fancy head
compartment with fine fittings and custom-
color porcelain, the plain white, no-nonsense
Lavac looks a bit out of place. (Also, it’s avail-
able only in white.) This has been one of the
most common reasons that my office has in-
stalled other heads in larger custom boats—
simply to better match the high-style decor of
the surroundings.
The Blakes Lavac comes in two models:
the lower-cost Popular and the higher-end
Zenith. They look nearly identical, but I
would use the Zenith on all but the smallest
boats. The Zenith model is intended for heav-
ier use. Cost seems to hover around $500
these days (2008), which is a very reasonable
price for a quality marine toilet.High-Volume Flushing
A more serious consideration is that the
Blakes Lavac toilet pulls a lot of water
through for each flush, or it can. Remember,
you’re using a true diaphragm bilge pump—
really a bilge pump. This is one of the reasons
that the pump is so unlikely to clog. You can,
however, stroke as many times as you like
with the lid closed. This will surely clear all
the effluent from the toilet and all the sewage
lines, which is a plus if you pump overboard.
With no effluent in the hoses, there’s no
smell. The drawback is that you can quickly
pump a holding tank full—something to be
wary of.PART SIX:PLUMBING SYSTEMS WITH NOTES ON FIRE SUPPRESSION
Toilet Water Usage and
Holding Tank SizeThe old standard landlubber toilet
installed in most homes and offices uses
3 .5 gallons (13.2 L) per flush. In most
places in the United States, new toilets
are required to use less than 1.6 gallons
(6 L) per flush.Marine toilets do much bet-
ter.The thriftiest marine vacuum-flush toi-
lets can average about 1.5 pints (0.7 L)
per flush.Most standard marine toilets use
between 2 and 3 quarts (1.9 and 2.8 L) per
flush.It’s been found that an average
individual is likely to flush a toilet about
8times per day.Thus for average toilets,
if you assume 2.25 quarts (2.1 L) per flush
and 8 flushes per person per day, that’s
4 .5 gallons (17 L) per person per day.
Four crew for five days between tank
pumpout would then be 90 gallons
(340 L).Switching to toilets that average
just 1.5 pints (0.7 L) per flush would reduce
the required black-water tank size to only
30 gallons (113 L).
You should size the holding tanks for
any boat this way.Determine the type of
toilet and the average gallons or liters per
flush.Multiply that by the average of
8 flushes per person per day.Then multiply
by the number of crew and the days be-
tween pumpouts to get minimum holding-
tank (black-water tank) size.