Greywater discharge installation

[Geardunkin]

The sink on my S2 7.9 is basically useless. The drain is plumbed to a greywater tank that must be removed to drain. I am considering adding a simple greywater discharge behind the sink and above the waterline (see attached photo). This is common practice here on the Great Lakes. A through-hull with a seacock hosed directly to the sink drain should do the trick, right? Any other considerations before I start drilling holes in my boat?

 

[Peggie Hall HeadMistress]

Sink drain thru-hulls are below waterline on almost all sailboats and that's where I recommend you put it to avoid upsetting any enviro-zealots who consider discharging gray water overboard as big a "sin" as flushing black water overboard. There are enough of those on the Great Lakes who misinterpret regs that only apply to large commercial vessels as applying to recreational vessels to make it worth the effort to stay off their radar. You're already planning to add a seacock, so there'd be no added expense.

As long as you're doing a little work on the boat, it would be a good idea to pick up some brackets and hang that fire extinguisher. It needs to be between the source of any fire and the exit from the boat, so that you can use it as you move toward the exit.

--Peggie

 

[Benny17441]

One reason, not to install a galley direct discharge is to avoid getting an ugly, nasty stain in the hull above the water line.

 

[Dalliance]

As long as the seacock is within easy reach, I see no issue. You may need to close it on certain points of sail if you heel too much. Mine is plumbed as you describe, with the through hull less than ½” above the resting waterline. I always close the seacock when I leave the boat, but have never needed to under sail.
If I was choosing my through hull location, I might go below the waterline as an aesthetic choice. Peggy makes an interesting point about dock Karen’s. I’ve had no issue to date, but you never know.
When I bought my boat, the existing lav sink drain had a dubious old white nylon through hull and there was no seacock! One of the first things I did was replace that hazard with a new bronze through hull and seacock. It just made sense to use the existing hole.

 

[Tally Ho]

My sink discharges through a thru-hull with a ball valve. The thru-hull is not low in the hull, but it is below the water line. 1 issue with having it near or above the water line is that there is not a lot of head pressure to drain the sink quickly. It will drain, but it is slow.

Greg

 

[Tally Ho]

One reason, not to install a galley direct discharge is to avoid getting an ugly, nasty stain in the hull above the water line.

What kind of stuff are you washing down the drain


Greg

 

[Peggie Hall HeadMistress]

My sink discharges through a thru-hull with a ball valve. The thru-hull is not low in the hull, but it is below the water line. 1 issue with having it near or above the water line is that there is not a lot of head pressure to drain the sink quickly. It will drain, but it is slow.

That kinda goes with a below waterline sink drain 'cuz there's always water in the drain line to the waterline pushing back. It's a small problem to deal with compared to cleaning the stain off the hull below an above waterline thru-hull. If it's really a problem a plunger can help.

--Peggie

 

[Geardunkin]

Thank you for the responses! It sounds like below the waterline is probably the way to go, but I'm assuming that an anti-siphon valve is needed just to be on the safe side.

 

[RoyS]

Galley sinks should be near the centerline of the boat to prevent seawater backing up and overflowing the sink when heeled. Alternatively, an edge mounted sink should be raised up high enough, if possible, to prevent this problem. As Dalliance mentioned, with your existing sink you would have to close the drain seacock while sailing. Do not forget!

 

[Scott T-Bird]

Thank you for the responses! It sounds like below the waterline is probably the way to go, but I'm assuming that an anti-siphon valve is needed just to be on the safe side.

No, I can't think of a reason for an anti-siphon valve or a vented loop if that is what you are thinking about.

 

[Peggie Hall HeadMistress]

Thank you for the responses! It sounds like below the waterline is probably the way to go, but I'm assuming that an anti-siphon valve is needed just to be on the safe side.

No no! 1. siphons can only be started in a line through which water is being PULLED...that's not happening in a sink drain.
2. drains should be as straight downhill as possible without any uphills between the sink and the thru-hull...P-traps and valves just create problems. Keeping the seacock closed except when the sink is in use is all that's needed "to be on the safe side." Or you can just keep a rubber plug (Walmart sells 'em) in the sink to prevent water from being forced up the drain when underway from turning the sink into a fountain.

--Peggie

 

[Tally Ho]

What Peggy said…

No anti-siphon is needed, but you should get in the habit of closing your thru-hulls anytime you are away from the boat.

I had a close call…..and now routinely close my three valves whenever I leave the boat.

Greg

 

[Peggie Hall HeadMistress]

Just how old WAS that hose, Greg?

--Peggie

 

[RoyS]

I advocate for a stress test every Spring to all thru-hull hoses. Grab it and pull in all directions. If the hose survives that you should be good for the season.

 

[Tally Ho]

Just how old WAS that hose, Greg?

--Peggie

I don’t know…boat was built in 1988…so could have been 35 years old

Worse yet, I owned her for 5 years before I noticed it and replaced it.

But it is all good now and I am sleep at night.


Greg

 

[Tally Ho]

I advocate for a stress test every Spring to all thru-hull hoses. Grab it and pull in all directions. If the hose survives that you should be good for the season.

That certainly would have exposed my bad hose.

Great suggestion.


Greg