"Head 101" topic --- question about freshwater flush plumbing

[Noah]

Hey- Stu, I was looking at a Head 101 topic you post in 2010- on swapping the sink drain hoses and shower sump hoses on their thru-hulls to facilitate fresh water flushing and perhaps I am dense, but doesn't this set-up result in all grey water from the head sink ending up in the holding tank? If so, I am not keen about adding additional gallons to holding tank, that otherwise would go out the thru-hull. Or does gravity still drain the sink out the thru-hull. If hopefully so, am I right in thinking that the last flush of the day (freshwater) is accomplished by CLOSING the thru-hull and running water in the sink and pumping the toilet, and it will use the freshwater in the sink drain hose for the flush....or am I all confused?

Thx
Noah

SEE YOUR QUOTE /PROCESS BELOW
So, how about this:

Change the dual connection "head intake and shower sump" and simply SWITCH the shower sump out and the sink out?  It's just like a "T" and on my boat it's a straight into a 90 degree elbow.

Couldn't be simpler.

HERE'S HOW SIMPLE IT CAN BE

I did this today.  Simply swap the head sink outlet with the shower sump outlet on the thru hulls under the head sink.

The REALLY interesting part is that once I redid the hoses and connected the sink out to the head, when I opened the seacock, EVEN WITH THE HEAD SINK NOT STOPPERED UP, the head pump pulled the seawater through.

The ONLY downside is that now we have to open all three valves.  In the past, I used to leave the (formerly) separate head sink thru hull valve closed unless we were on the boat for an overnight or longer.  Big deal, great improvement, really simple.  Since we shower on board, we use the shower sump regularly.

Doing this, and only using freshwater for ONLY the LAST flush of the day, plus using Odorlos (NOT through the sink, only through the head), should make the smells disappear.

Only necessary for us saltwater sailors.

[Stu Jackson]

Two scenarios:

1.  You actually use the head sink for anything?    I find the headroom useless, so we use the galley sink.  But, if indeed you do use it, it will drain overboard since the head valve is in the dry bowl position and the hose from there to the head is full of water, so the gray water does go out of the boat and not into the head.

2.  For the last flush of the day before you leave the boat, you run clean fresh water through the head sink faucet into the sink, I find filling the sink halfway works up enough for six strokes, and then pump the head.  Clear water to head.

[Noah]

Do you close the thru-hull before the fresh flush? Otherwise I would think it would suck in seawater.

[Ken Juul]

yes close the thru hull, fill the sink, pump till empty.  It also helps to put a stopper in the head sink when you want to do a sea water flush.  I use one of those round rubber sheets sold to help open stubborn jar lids.

[Noah]

Great! Thx. I will give it a try.