Steve Lusardi wrote:
Toilet to tank, toilet overboard and through hull.

What you really need for that are diverter valves (aka "y-valves"). And
I'd only go with Whale...'cuz Whale pumps and y-valves will last almost
a lifetime if maintained. I did a little googling for 'em on your behalf
and found for $64.95 at this retailer:
http://www.discountmarinesupplies.co...TER_VALVE.html
Mfr's list price: $89. West Marine's price: $93

Plus pipes and hose. I am
aware of PVC of course, but I'm not certain of its durability or its
permeability by vapors and toilet gases.

I'd stick with hoses. PVC is odor impermeable, but can be problematic.
It's only recommended for long straight runs...'cuz radius fittings and
unions are needed when it has to go over, under, around anything. Every
connection means a bump in the road where sea water minerals, solid
waste etc can get caught and build up. It doesn't flex much either, so
it has to be well supported and "soft coupled" to anything rigid
(toilet, tank, thru-hull etc) to provide shock absorption. Hose otoh,
bends a lot further and doesn't mind shock and flex. Trident 101/102
would be my choice. It's a double-walled hose, available in either black
or white, that has a biocide in the rubber formulation...which makes it
the most "bullet proof" hose on the market today. A bit pricy, but
worth it IMO. http://www.tridentmarine.com/stage/sanitation.htm

These are valves made from a fiber
reinforced plastic that is popular in the chemical industry. I am not aware
of its name, but it is much stronger than PVC.

They're prob'ly pretty rugged, but no more so than a Whale. Plus, you'd
need two ball valves (close one, open the other) and a somewhat complex
plumbing arrangement...only one y-valve (just turn the handle) and
plumbing that's very straight forward.

However, if you also need a seacock for the thru-hull, a ball valve is
the ONLY thing to use--no gate valve! Either bronze or Marelon. But I
wouldn't use bronze in any other part of the system.

And, you'll need a couple of vented loops (siphon breaks)--one in the
toilet intake, another in the toilet discharge.

In fact, it might be a good idea if we could discuss your whole proposed
installation in detail. Is your email address valid if the 'nospam' is
removed?

--
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://shop.sailboatowners.com/boat_odors/