rhys wrote:

I've done this on my Great Lakes boat with no problem. I have (from
the hull up)

a seacock,
a six inch piece of marine hose (double clamped both ends)
a reducing T-fitting to a 3/4" water intake to the head (just below
the waterline and double SS-hose clamped)
about a 12 inch length of double SS-hose clamped marine hose
a plastic ballcock with appropriate barbs
a short length of clamped hose going into the drain pipe (about 10
inches) of the head sink.

Methodology is as follows:

Normally, both seacock on hull and the plastic ball valve are CLOSED.

When I want to use the head, I reach into the space beneath the sink
and open the seacock. The hoses fill with water, slightly under
pressure as the entrance is about 18 inches beneath the waterline.

I use an old Brydon manual head that's about kaput, but it works for
the light duty I subject it to.

When finished, I flush to a 30 gallon holding tank.

I close the seacock.

To empty the sink, I simply open both the plastic ball valve and the
seacock. Grey water leaves the boat. I suppose a smidgen might get
into the head intake pipe, but visually, at least, this is not an
issue.

No problems in three years with this, except for a visit to the
Travelift when the seacock split due to "failure to winterize
properly" by me.

If Peggie says this is OK, feel free to swipe this "design".

Works ok for me.

Obviously, an offshore set-up would be simpler, but I flush WITH the
lake, not INTO the lake G.

Actually, you don't have a choice...it's illegal to flush directly
overboard--or dump a tank--in any US and most Canadian inland waters
including the Great Lakes. You must be out to sea at least 3 miles from
the nearest point on the whole US coastline to legally do either.

The only thing at issue, though, is where the DISCHARGE from the toilet
goes...the flush water source doesn't matter. So there's no need to
"secure" an intake thru-hull in any waters, only any overboard discharge
thru-hulls and/or y-valves coming OUT of a toilet or tank.
--
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://69.20.93.241/store/customer/p...40&cat=&page=1