holding tank fills itself

[Mickey84H34]

The holding tank on our Hunter 34 keeps filling up with sea water while we're away from the boat. We're in a marina so the pump-out seacock stays closed all the time and the sea water intake for flushing gets closed whenever we leave the boat. What could be going wrong?

 

[Steve Dion]

Gremlin's?

 

[kloudie1]

Strange one, Mickey.. My thru-hull for the overboard pump has a loop that goes up to just under the deck and has an anti syphon valve in it so there really is no way to get seawater back to the tank. If you have the same big loop, it would be really difficult to get seawater back to the tank.. If no loop, a valve leak would do it. Do you have a "Y" valve that bypasses the tank for direct overboard?? If that doesn't have a loop between thru-hull and tank, a valve leak again could put water in the tank. Hope ya find it !!
(I hope it isn't the pianist sneaking aboard at night!)

 

[kloudie1]

Head Plumbing

Like this: Furthest outboard black hose goes straight to tank top fitting. Red hose to left goes straight to pump out fitting on deck.. Discharge from the yellow handled hand pump goes up to anti-syphon loop then back down to thru-hull. Peggy, the missing loop that might be in the line between the bowl and the flushing pump is not necessary here since the top of the bowl is above the local waterline.. I don't worry about it when I am there.

 

[Bill Roosa]

Discharge through hull

You mentioned the pumpout, the head intake but not the discharge thru-hull. Normally the macerator plugs the hose between the tank and thru-hull to the sea so nothing can come backwards through it. If the impeller has a missing vane though it will pass water.
Try closing the macerator thru-hull

 

[KMm]

Re: Discharge through hull

You said you close the thru hulls, But if there gate valves not ball valves many times the gate will act as it is closing but still let water pass. Just a thought.

 

[Ron20324]

A slip neighbor had the same problem. A hose from the holding tank went to a macerator, then to a thru-hull he couldn't see, so never closed. It back-filled into the holding tank. Thru-hull closed, end of problem.

 

[Tim R.]

I had a Marelon valve on my previous boat that felt like it was closing but the handle was broken off the internal ball.

 

[Peggie Hall HeadMistress]

Only one way sea water can get in:

Through an open or leaking seacock on a below-water thru-hull that's connected to plumbing that's connected to the tank. In a sanitation system, that provides two possibilities: the thru-hull used to dump the tank at sea (no vented loop between the pump and the thru-hull), or--unless you've installed a toilet that uses onboard pressurized flush water--the head intake thru-hull--a leak that's allowing seepage so slow that it's able to exit the bowl instead of filling the bowl and overflowing. This is even more likely if you haven't replaced the joker valve in the toilet in at least two years.

It has to be one or the other.

 

[Mickey84H34]

The pump-out thru hull does have a loop with siphon breaker valve so I'm thinking that the flush-water intake line is letting sea water drain slowly into the bowl and then out to the holding tank. I guess the "Joker valve" is suppose to prevent that from happening and it's a relatively new toilet but it's also a relatively new problem so that valve is the primary culprit. Any easy way to test that valve?

 

[Peggie Hall HeadMistress]

That's not the right way to fix it!

If the joker valve can't let the water out of the bowl, the bowl will overflow...and keep on overflowing till it sinks the boat if allowed to to continue long enough.

The RIGHT fix: 1. Close ALL seacock when you leave the boat! Open seacocks when no one is aboard is a leading cause of boats sinking in their slips. But even if a hose slips off a thru-hull, water cannot get in through a closed thru-hull. If you are closing 'em, the head intake seacock is most likely leaking...which is what makes the 2nd step in the right fix VERY important on any boat:

2. Install a vented loop in the toilet intake.. Do NOT put it between the thru-hull and the pump...it'll prevent the pump from priming. It has to go between the pump and the bowl as shown in this photo. Priming a toilet pump--manual or electric starts a siphon. The vented loop is a siphon break that also puts an arch in the line far enough above the waterline to prevent water from getting over the top of it into the toilet bowl. The means it needs to be at LEAST 6-8" above the waterline AT ANY ANGLE OF HEEL, not just when the boat is at rest...which is why the one in the photo is so high. And btw, although the toilet in the photo is a Jabsco, installing an intake vented loop is the same for ALL manual toilets.

However, although a new joker valve is not the right fix for your problem, joker valves are important to the operation of all manual toilets and therefore should be replaced at least every two years--annually is better--as preventive maintenance. If it's been much longer than that since yours has been replaced, the slit in it will have stretched enough that it's no longer closed tight and may even have become a gaping hole. Or it may be encrusted with sea water minerals.