Sink outlet seacock question

[Boo2]

Does seawater flow into the sink? If not, it's above the waterline.

I think it's unnecessary expense and complication.

There is no water flowing into the sink atm but as I said it has a manual diaphragm pump so that may act to prevent that anyway.

I wonder if you're heading for syphoning problems with a pump delivering to a potentially submerged outlet over a looped pipe.
If you operate the pump whilst the outlet is submerged, there is a possibility of a back-syphon starting up when the pump stops, if the pump valves aren't tight. With sink waste going through them, that seems quite likely.
A syphon break seems to be called for.

Actually, I've just realised the sink position is a bit of a red herring because the new holding tank will certainly be below the water level so I think I do need a vented loop.

Boo2

 

[Tranona]

Not sure why you need a holding tank on your sink waste. Very unusual and unnecessary. As others have said, just drain it through a seacock at waterline level with the shortest possible run.

 

[prv]

Not sure why you need a holding tank on your sink waste. Very unusual and unnecessary. As others have said, just drain it through a seacock at waterline level with the shortest possible run.

You do find it mentioned on American blogs and forums - the idea seems to be to minimise the number of seacocks by draining all grey water into a sump tank by gravity, and then pumping it out through one single seacock, which can even be above the waterline if you don't mind a dribble down the topsides. The pump is controlled by a float switch, so it's not really a holding tank as such.

Agree that it's unusual and unnecessary in this installation (since it's not reducing the seacock count) and if the OP doesn't have a clear and definite reason why he wants it then he probably doesn't.

Pete

 

[sailorman]

You do find it mentioned on American blogs and forums - the idea seems to be to minimise the number of seacocks by draining all grey water into a sump tank by gravity, and then pumping it out through one single seacock, which can even be above the waterline if you don't mind a dribble down the topsides. The pump is controlled by a float switch, so it's not really a holding tank as such.

Agree that it's unusual and unnecessary in this installation (since it's not reducing the seacock count) and if the OP doesn't have a clear and definite reason why he wants it then he probably doesn't.

Pete

More questions than answers

 

[Boo2]

Not sure why you need a holding tank on your sink waste. Very unusual and unnecessary. As others have said, just drain it through a seacock at waterline level with the shortest possible run.

You do find it mentioned on American blogs and forums - the idea seems to be to minimise the number of seacocks by draining all grey water into a sump tank by gravity, and then pumping it out through one single seacock, which can even be above the waterline if you don't mind a dribble down the topsides. The pump is controlled by a float switch, so it's not really a holding tank as such.

Agree that it's unusual and unnecessary in this installation (since it's not reducing the seacock count) and if the OP doesn't have a clear and definite reason why he wants it then he probably doesn't.

Yes, that's the setup. I want a holding tank so I can have a sink in the heads that drains by gravity into it. The tank pump is going to do double duty as a bilge pump when ashore for winter because it is a diaphragm pump and won't suffer from the drawback of leaving a couple of inches of water in Sunrunner's very shallow bilge - hopefully this will help with the damp smell and mildew over winter.

Boo2

 

[Boo2]

I don't really understand the surveyor's point. Yes, if the sink pipe leaked below the waterline then water would come in until you closed the seacock - but the same applies to the cockpit drain hose too. I guess if there's a long run of sink pipe through lockers etc then it's more vulnerable than a short vertical run of cockpit drain pipe, but I'm assuming the reason they're teed together is that the sink is on the aft bulkhead of the cabin, right next to the drain.

The current sink drain does have a very long run from the sink behind the cooker heading aft to a point that it can cross into the engine compartment below the sole boards then forwards to the T joint in the cockpit drain.

It's a fair point as to how much more dangerous this is than the cockpit drain on its own though...

Boo2

 

[sailorman]

Yes, that's the setup. I want a holding tank so I can have a sink in the heads that drains by gravity into it. The tank pump is going to do double duty as a bilge pump when ashore for winter because it is a diaphragm pump and won't suffer from the drawback of leaving a couple of inches of water in Sunrunner's very shallow bilge - hopefully this will help with the damp smell and mildew over winter.

Boo2

we have a diverter valve in the head basin waste that is combined with the loo intet, so all basin waste is gravity fed into the loo bowl then pumped out. it has the benefit of also lubing the loo valves too

 

[Tranona]

Yes, that's the setup. I want a holding tank so I can have a sink in the heads that drains by gravity into it. The tank pump is going to do double duty as a bilge pump when ashore for winter because it is a diaphragm pump and won't suffer from the drawback of leaving a couple of inches of water in Sunrunner's very shallow bilge - hopefully this will help with the damp smell and mildew over winter.

Boo2

Then have a dedicated bilge pump and drain the washbasin through either its own seacock or into the toilet bowl as per Sailorman. Keeping the bilge dry in the winter is more of a job for an automatic electric pump rather than the complication of having a holding tank.