Dennis Gibbons wrote:
Peggy,
Have you ever heard of the following setup:
The waste tank is ABOVE the water line with a bottom drain to a
seacock.
There is a second drain from the top of the tank to the deck pumpout.
The head pumps up to the top of the tank.
Close the seacock in protected water to keep the bad stuff aboard and then
open the seacock when you get out.When offshore, simply leave the seacock
open to drain as you go (so to speak).

That is _nearly_ exactly the set-up that I have, with one important
modification, see after Peggie's comment.

Peggie Hall writes:


I'm not crazy about that set up. When the seacock is closed waste has
to sit in the line to thru-hull, permeating the hose...any sludge in
the tank will end up in that hose, so if you're in coastal waters very
long, that can cause problems

Right. So what I did is to have a PVC ball valve right at the drain,
then go with sanitation hose (the good one, of course) to the
seacock. Both the PVC ball valve and the seacock are usually closed
and only open off-shore for draining the tank. Thus, the hose ONLY
ever contains sea water (or antifreeze, in winter), except for brief
periods during draining. And after draining the tank I would pump
enough sea water through it (using the existing pump, i.e. through the
head) to make sure it is clean before closing both valves again. Just
like you pump fresh water into the tank when pumping it out.

Of course, I have never done it so far since I was always within 3
miles.

...and I can't see any reason to go
through a tank at sea instead of flushing directly overboard.

Oh, reason is options, and simplicity. I can sail legally in coastal
waters and without problems off-shore. True, having some construction
with Y-valves, or additional pumps and dip tubes would also work (and
actually have some advantages), but this setup is far simpler.

If the
tank vent should become blocked, you'll have problems flushing the
toilet due to the backpressure. Worst case would be a blocked tank
vent AND a clogged overboard discharge hose at sea in 8'+.

--
Peggie

OK, this part I don't understand. Why would a second drain block the
vent(s)??

--Ernst