Heads syphoning

[Jules]

Without looking through loads of manuals can anyone kindly tell me why Jabsco head is syphoning enough water to fill holding tank overnight? Should there be a S break in an upward loop?
I've tried closing the inlet and it still happens!
Thanks a lot

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[cliff]

If you have closed th einlet and it is not passing then logically the water must be coming in the discharge not through the head inlet.

When you pump out and "dry bowl" then any siphon is broken. Does the toilet bowl fill during the night?

I assume you have routed both the inlet and discharge to/from the head in in loop to just below deck level as per the installation instructions.

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[steve_cronin]

Yes , an air induction valve in a loop extending up above the waterline and the holding tank is the ideal. Most boats get away with relying upon the last user to pump out until an air break is created in the outlet loop. Not all "seacocks" seal completely especially if some "foreign" matter is allowed to breach the seal of modern ball valves by not pumping until absolutely clear water is being flushed out.

Steve Cronin



<hr width=100% size=1>The above is, like any other post here, only a personal opinion

 

[Jules]

Thanks. It is a 4yo boat and only started doing it last year. It does fill the bowl, but more slowly though. I'll try pumping until clear as routine.

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[HeadMistress]

The head isn't siphoning...water outside the boat is simply seeking its own level inside the boat.

Although a vented loop in the head discharge line is necessary for below waterline toilets that flush directly overboard--to prevent sea water from backing up into the toilet--in toilets that only flush into a tank, a loop in the head discharge line only helps to prevent backflow from the tank from running back into the toilet...it does nothing to keep seawater out the bowl.

However, when your head INTAKE through-hull is open, if there's no vented loop in the head intake line, that's the most likely source of the water. Relying on the wet/dry valve to stop it is an excellent way to sink a boat in its slip...because a) people leave them in the wet mode, and b) the d'd things fail--which is apparently what's happened here. Installing a loop in the intake not only creates a siphon break, but also creates a "hill" above the waterline ...keeping water out of the bowl because water will only rise TO the waterline.

A loop in the head intake should NOT be installed in the line between the thru-hull and the pump...putting it there will interfere with the pump's ability to prime. It has to go between the pump and the bowl--to replace the short piece of 3/4" hose from the top of the pump to the back of the bowl--and should be at least 8-12" above the waterline at any angle of heel.

There is one other possible source of the water: if the tank is plumbed to be dumped at sea, and if the tank is at or below the waterline without any loop above the waterline in the line going to the thru-hull, water will rise in it to waterline...a macerator will slow it down, but won't prevent it. Wherever the tank is in relation to waterline is how far water will rise inside the tank. The cure for that is a loop between the macerator and the thru-hull and making certain that the seacock always remains closed except when actually dumping the tank.

While vented loops do provide some protection, I strongly recommend that you close all seacocks when leaving the boat.

<hr width=100% size=1>Peggie Hall
Specializing in marine sanitation since 1987

 

[fluffc]

If you've not got a syphon break in both lines (in and out), then i thoroughly recommend fitting one. Boats have been known to sink because of this problem. Just fitted a pair on my boat after discovering a syphon problem when seacocks were left open.

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[Jules]

Peggy,
the boat is a 1999 US Hunter 310. Fitted with a direct discharge and a holding tank. either is selected via a Y valve. The holding tank appears to fill over a 6-8 hour period if all thru-hulls are left open. This started happening last year.
This is a bit annoying as when we are living aboard the tank does not just have "what it is supposed to have" in, but a load of seawater as well. Should the outlet / inlet from the tank have a one-way valve? The bowl appears to fill as well, but much more slowly, perhaps 2 pints overnight.
Thanks for your help

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[HeadMistress]

I'd bet real money that the head intake is at least one of the sources of your water. Without a loop in the intake above the waterline, water will rise in the bowl TO the waterline. That couple of pints that you see in the bowl are only what hasn't seeped out of the toilet into the tank yet.

If there's no loop in the line going from the tank to the through-hull, water is rising to the water line via that line too...filling the tank.

A one-way valve won't solve it, it will only create another set of problems. Only two things will solve your problem: keep the seacocks closed except when actually in use...or, if that's not practical for you as a liveaboard, vented loops that are at least 8-12" above the waterline at any angle of heel in ALL lines connected to below-waterline through-hulls.

If the thru-hull through which the tank is dumped is the same one used by the toilet for direct overboard discharge, I would also recommend that you replace any tee or wye fitting in the tank pumpout/discharge line with a y-valve and keep it aimed toward the deck pumpout at all times except while dumping the tank. If the tank is dumped through a separate through-hull, keep that seacock closed at all times except while dumping the tank...'cuz there's no reason for it to be open except to dump the tank.


<hr width=100% size=1>Peggie Hall
Specializing in marine sanitation since 1987

 

[Jules]

Thanks for your help all.

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