Holding tank keeps filling

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PDX-Boats

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Anyone experienced this..
I just did a pump out last time we used the boat. We've hardly used the head and it's fine from empty to full.
My first thought was a leak from the fresh water, but you'd think we'd hear the fresh water pump no cycling if that were the case.
I'm perplexed.
 
If you have an overboard pump-out ability, it may be backfilling when running. There should be some sort of backflow preventer like a flapper, or check valve or even a simple clamshell cover. You can tell if the tank has pure saltwater in it or the real thing by tasting it.o_O
 
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Mmmmmm,,,,, Halfhitch,,,,, stick your finger in the toilet and swirl it around then taste???? I'll pass!!! :oops:
 
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If the holding tank discharge seacock is left open, there's a good chance water will enter the holding tank when you're running at planning speed. Just like when your livewell fills up when the seacock for it is left open. Just my two cents...
 
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I've been doing pump outs.
The sea chock for overboard discharge is closed.
Just did a fresh pump out this afternoon. We'll see how far that goes
 
Is it "full" based on a gauge or based on you looking at the tank? Either of those could be misleading... floats for the senders can stick... tanks can "look" full based on discoloration on the inside.

It may help to know the year/model of boat.
 
2008 Express 305.
I'd thought about a malfunctioning gauge too, but yesterday the tank was clearly full. (Water to the bowl).
 
What kind of system is it? Vacuflush? You said you were initially thinking of fresh water filling the tank.

Can you elabaorate on what "water to the bow" means and how you're thinking this plays in with a full tank?
 
It's a VacuFlush head.
What I'd meant by "water to the bowl" was that when I depressed the flush lever, you could see standing water in the toilet bowl. Couldn't flush the toilet because the tank was full to the brim.
Again, we'd hardly used it. Very confusing
 
OK, making more sense, now. Now, the "water to the bowl" could simply be due to a clog... whether it's from an agressive eater or wiper or things being flushed that shouldn't have been.

Are you 100% sure the tank was ACTUALLY full or were you basing that on other factors (like the water backing up in the hose)?

Edit/adding... it's extremely unlikely that the tank is actually filling up. If the sensors are working, they will electrically interupt the vacuum pump - and you would know that since you wouldn't hear the vac pump running when you first turn the key on. Plus, there are one valves inside the vac motor to keep black water from flowing up to the toilet. On top of the that... you would have first fill the holding tank, then fill the vac tank... there's just too many things that would have to be overcome to allow this to happen. A clog is the most likely culprit, making you "think" the tank is full, when it really isn't.
 
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If my tank is full the electric flush will continue to pump to the point that the tank will overflow thorough the pumpout cover on the deck. Did experience any over flow?
you
 
While we’re on the subject of “head operation” and an FYI - the mushroom head on the hull that serves as the vent hose exit, has a metal screen on it. Over time the screen can clog to the point that the venting function stops. This can cause a real mess when you pump out and pressure builds unchecked in the tank. I punched out the screen and all well again.
 
On my vacuflush, when the tank is full the vacuum pump is disabled so it cannot be overfilled. The discharge pump has two duckbill valves that will prevent water from the hull overboard discharge from coming back into the holding tank when on a plane. Does your discharge pump run when you are trying to pump out overboard? If you see water not moving when you flush and the vacuum is not there, then the holding tank is really full or there is blockage between the bowl and the holding tank. Typically these type issues are related to the duckbill valves (4 for vacuum pump and 2 for discharge pump). Try discharging with the seacock open. If you don't see any discharge, then either then tank is empty or your discharge pump and associated duckbills are not functioning properly. I'm guessing your tank is full and the discharge system is not right. The vent can cause issues as well. Unless you have a leak in the fresh water valve at the toilet itself, a leak on the flush seal will let the bowl go dry and cause the vacuum pump to cycle.
 
I had a similar problem last year with having to pump out the holding tanks more frequent than previous years. One thing I checked is the ring gasket around the pump out cap. Mine looked a little deteriorated and rain water may have been the culprit. I changed the cap and gasket at the end of the season and will see how this year goes. Hoping my problem is resolved.

Link to thread in case there is any additional information for you:

Vacuflush Head Help

This is my third season with a Vacuflush Head on a 2005 Marlin. We use it lightly, and the first two years I only had to pump it out at the end of each season. This year I've already had to pump it out 3 times. Couple things I've noticed. First I hear my water pump prime without water use...
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