How does a sink drain work?

[jarcher]

On my boat, there is a thru hull below the water line. The drain from the sink in the gally goes directly to it. So, that means the sink never actually drains. As near as I can tell, that thru hull is useless.

I was thinking I could drain the sink into a small holding tank with a float triggered bilge pump in it.

Or, is there any reason not to just drain it into the bilge and let the bilge pump take care of it? I hardly ever actually use the sink anyhow. We mostly store beer in it

[Faster]

Yeah, but if a beer can leaks you'd have beer in the bilge..

The water level in your sink drain will, of course, be at the waterline level. If the bottom of your sink is close to waterline, then the sink will barely drain, ie water in the drain line will always be there. - If your sink actually won't drain at all, then it's either too low in the boat (or too deep for that location) or the drain line is plugged somewhere.

Also if the sink is a ways off centerline then you're probably going to get water back into the sink when heeled towards that side. On many boats one of the pre-sailing routines is to close such sink through hulls (galley and/or head) to avoid a wet surprise the first time you tack.

Adding a tank/pump sounds unnecessarily complicated.

[kaluvic]

I wouldn’t drain it into the bilge...its just so nasty...imagine everything that’s left on your plate when you finish eating, all over your bilge...the oil is probably the worst.
Is it possible to plumb the sink to a holding tank that is above the waterline so you can drain it over the side via gravity.
If you can do this its so sweet...you will need to put a P or bottle trap between the sink and the tank....you'll also need to vent the tank.

[erps]

Your sink at home always has water trapped in the drain too, in the P-trap. I would leave the sink drain alone and sand some teak instead.

[jarcher]

Originally Posted by Faster

Also if the sink is a ways off centerline then you're probably going to get water back into the sink when heeled towards that side. On many boats one of the pre-sailing routines is to close such sink through hulls (galley and/or head) to avoid a wet surprise the first time you tack.

Adding a tank/pump sounds unnecessarily complicated.

The botom of the sink is probably not far above the waterline at all, and yes, when I heel the sink can fill. I just closed the thru hull and have not opened it, since I rarely use the sink.

Since the bottom of the sink is so low I don't see how a gravite fed extra tank would work, but I am probably missing something.

I suppose I could also lower the thru hull? If I do that woudl the sink actually drain when the boat is sitting still?

[klem]

Lowering the thru hull will not make any difference. What matters is the height of the sea water relative to the height of the bottom of your sink. The two of these should equalize rather quickly. If they are not, you probably have an obstruction in the drain somewhere. I make a habit of using draino from time to time in sinks to clear them out. I suspect that if you were to close the seacock and take the hose off, it would be pretty plugged up with stuff. I have even had to snake drains from time to time.

I don't recommend using a gray water tank if you can help it for the same reason that the line is giving you problems. Lots of grease and coffee grounds tend to go down sinks and are very hard for small pumps to deal with and they slowly fill up the tank. If you use a gray water tank, you will need to open up the top from time to time and manually clean it out. On the commercial boats that I worked on, it was common practice to fully clean all black and gray water tanks twice a season and many people preferred to do the black over the gray. There is nothing like having a pumpout clog and then needing to unclog it while the tank is full.

[xact]

You pour draino into the water?
great makes me want to be swimming around your boat

[jarcher]

Okay Klem, thanks, I see what you all mean now. I'll check for clogs. That should be easy enough, now that I'm on the hard I'll just pour some water into the sink and see how quick it drains. Replacing a few feet of tubing should be easy enough as well.

[sailingdog]

I'd recommend you leave it alone. A grey water tank will become a maintenance nightmare in short order.

[Sabreman]

Could also be marine growth in the through hull. We routinely clear them when we haul for the winter. There always barnacles hiding up in the hole. A quick, easy way to clear a clog is to blast it with a jet from a hose. Of course, you could end up with a face full of water. We also use a length of clothes hanger to open clogs (the drain hose should have few if any bends).