http://www.lavac.com/

I found the website of the really great marine head installed on a
racing trimaran that's visiting Charleston this week. After struggling
with those cheap plastic crappers from Waste Marine all clogging and
sticking plastic valves and the damned pumps that you have to keep
greased....THAT STINK....

If you've never seen this toilet, or used it, or flushed it, look out
for it....

The model installed on this spartan trimaran is the simplest thing I've
ever seen. The seawater seacock through the hull is right behind it and
there is a water loop with an anti-siphon U in the top of it because in
this boat the toilet is far below the waterline and would flood the hull
otherwise. There's NO PUMP, NO PARTS, NOTHING MOVING in the head,
itself! The head is simply plumbed with plastic bilge pump hose to a
regular Whale diaphram bilge pump surface mounted high on the bulkhead
behind and to the side of it so you don't bump your head while seated.
The outlet of the pump goes into the Y-valve to select sanitary tankage
or overboard discharge. After the pump, it's the same old sewer system
any boat has....way too small to hold much for long.

You have two choices to flush....

Leave the seat OPEN and it merely pumps out whatever's in the bowl until
it sucks air....LOTS OF AIR! That diaphram pump isn't that crappy
little plastic pump on the head you have now...and it works SO EASY WITH
SUCH A SHORT LIFTING HOSE...ABOUT 3' so the pump is ABOVE the waterline
and can't backfill the boat if one of its valves is stuck open. If you
want to use up your fresh water to flush with the shower head, this
allows it just fine.

Leave the seat CLOSED and it's a full-blown, self-flushing vacuum toilet
because the seat seals to the toilet and the lid seals to the seat VERY
TIGHTLY WITH A SOFT PLASTIC SEAL ON BOTH ON THE BOTTOMS. You hear a
sound that sounds like one of those tankless gas station toilets
flushing when you pull the big handle on the 1" water line that feeds
them! This puppy flushes HARD on that much vacuum from the Whale pump!

Running on 1 atmosphere of PRESSURE, 14 PSI, I don't think ANYTHING that
can be sucked down that tube could EVER clog it up!

Now the important part......IT SAYS SUCKED SHUT VERY TIGHTLY AFTER THE
FLUSHING STOPS! The suction comes from an intake valve that won't let
the toilet flow go backwards towards the seacock. As this valve, which
must be a simple flapper, is on the seawater side, nothing in the toilet
will clog it up and with this much pressure I cannot imagine anything
from the sea stopping it from opening.

To flush you need only close the lid and make TWO pumps on the Whale.
Now SEALED, the toilet CANNOT SMELL UP THE BOAT! God, where was this
when I used to have to stand watch downwind from the stinky heads in
cruising boats?!