wrote:
Typically, two adults aboard. Although there will be guests, it will
not be the norm. There will be passages, and yes, I would like the
ability to flush directly overboard at sea. Knowing my propensity to
put my feet up and just sit back and enjoy the world I should
prepare for extended stays in an anchorage. That said, I don't mind
a trip offshore or to a marina once in a while. Frankly, with the
size of the vessel I'm afraid to try to build too much storage
capacity into the head system. I just don't foresee having the
equipment and stores for two people stuffed into a 28 footer to last
for several weeks of independent anchoring.
Woohoo...at last! Someone who isn't asking what size tank he needs to
install to last 4 people at least a month! 
(The answer to that one:
300 gallons.) Hokay...here's what I recommend for you and your boat:
Since you want the ability to flush directly overboard at sea, I would
not go with a self-contained system...there's no way to bypass the tank
to flush directly overboard. So I think your best bet is a
straightforward manual marine toilet and holding tank with y-valve that
offers a choice of flushing directly overboard or into the tank.
Toilet: either a Lavac manual or a Raritan PH II.
Tank: 20-25 gallons...best source: Ronco Plastics
(http://www.ronco-plastics.com) They make top quality plastics tank for
a very reasonable price and have over 400 shapes and sizes to choose
from--more than 100 of which are non-rectangular. And they install
fittings in the sizes and locations specified by the customer when they
make the tank.
Hose: AVS96 (
http://www.aussieglobe.com/avs96.htm) Proven in independent
testing to be at least 16x more resistant to odor permeation than any
other hose on the planet...$5/ft cut to any length direct from the mfr.
Btw, this is the same hose that SeaLand distributed exclusively in the
US for several years as their brand name "OdorSafe." Since being bought
out by Dometic SeaLand hose is now made by an Italian mfr, and the
Australians are now selling their hose here themselves.
Y-valve and manual overboard discharge pump: Whale.
Can you refer me to a prior post of yours in which you discuss
appropriate head storage capacity?
Easier to just tell you here than hunting it down: the average adult
uses the toilet 5x/day...average flush: .5 gal. So each person
continuously aboard will put 2.5 gal/day into a tank. A 25 gal.
tank--which is about the max size that makes sense for a 28'
boat--should last 2 people 5 days of continous use inside the "3 mile
limit."
Which is why, if it were my boat, and my budget could stand it, I'd
install a Lectra/San (CG certified Type I MSD that treats each flush and
discharges it overboard legally--and without harm to the environment).
The power consumption--1.7 ah/flush--sounds scary, but actual daily
consumption for two people is only 10-12 ah/day...not much at all. That
would allow you to install a much smaller tank (10-12 gallons) that
you'd only use if/when you were to visit one of the few "no discharge"
harbors on either coast...and there aren't many--only a few small ones
on the whole east coast between RI and the FL Keys...only one--also very
small--north of Santa Barbara on the whole west coast...and only
two--the Keys and Destin Harbor--in whole Gulf. That makes the discharge
of treated waste legal in about 90% of US coastal waters...so why store
waste aboard and have to deal with pumpouts or going offshore if you
don't have to?
For installation specifics, I suggest you check out the link in my
signature...and of course, I'm always glad to answer any questions.
--
Peggie
----------
Peggie Hall
Specializing in marine sanitation since 1987
Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and
Other Sources of Aggravation and Odor"
http://www.seaworthy.com/store/custo...0&cat=6&page=1