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270 Cruiser VacuFlush 500 toilet with a VHT12 holding tank

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Hi All

I have a 2010 270 cruiser with a macerator pump fitted and am located in Australia.

I have trawled through a bunch of threads on this subject but have not yet found an answer to my specific question.

I have a VacuFlush 500 toilet with a VHT12 holding tank.

The system has not been used very much since the fitted when the boat was built.

I would like to test the 3/4 and full indications and full level cut out and just give the system a clean bill of health or understand what needs to be worked on. I plan to service it and carry out replacement of all the known parts that wear out (duck bills etc). I’d just like to understand if I have bigger issues than a routine service.


At the moment the toilet fills up with water when I lift the toilet lever up, the vacuum pump runs and then stops, so it looks like it is maintaining that vacuum. I am not 100% sure it always maintains that vacuum, but when I have run it, the vacuum pump stops running.

Flushing works and the flush goes through to the holding tank.

At this point the holding tank is pretty close to empty.

I see nothing discharging over board at the sewage \ bilge discharge vent at the water line (not sure if there is a common vent) which as expected it shouldn't.

I now wish to fill the holding tank with water by taking a hosepipe of fresh water into the toilet bowl, pushing the handle down and basically flushing all that fresh water into the holding tank until the 3/4 light comes on, and then the full light.

At this point the flushing should stop and be interlocked until the tank is discharged via the pump with the key switch in the head.

What I am seeing is that as I fill the holding tank up in the manner described above, once I get visually to around 50% of the holding tank the water discharges out the discharge vent at the water line. I thus cannot ever fill the holding tank in this manner. I know something is wrong but am not sure what has failed.

Can anyone please describe the process that should be followed to achieve this test and if I am making any incorrect assumptions.



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  • 1 month later...

If anyone is interested I figured this out:

  • I filled the holding tank by just repeatedly flushing the toilet. Trying to fill it with a hose in the manner I described didn't seem to work.
  • I did this until the 3\4 light switched on, so it was good to test that.
  • I also drew a small line on the side of the tank with a permanent marker where the 3\4 level is.
  • I took the full level switch out and cleaned it. It turns out this switch doesn't work. I tested it in a cup of water. However I tested the circuit by shorting out the pins to simulate a full alarm.
  • A full alarm does not interlock the operation of the toilet which I find a bit odd.
  • I would have expected the full switch to interlock the system. The Sealand \ Dometic dealer here thinks it should but has not provided me a wiring diagram to check it. I will look for a relay on the control panel in the head.
  • A new full level switch is very pricey for what it is. Has someone else been able to source this type from somewhere else?



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I recall when my vht12 was full full, it would not operate.  but at the time it was not really full, it was a multiple tampon issue.   i took it apart, removed the tampons (nasty job) and cleaned the indicators, i have 2 indicators like you, 3/4s and full.  I replaced  the duck bill valves, i was losing vacuum.  If you have full vacuum and then cut the power to the vacuum generator, when you turn the power back on the next day or next week, the vacuum generator will not run, unless there are leaks.

when you put it back together use some silicone. i recall vaseline was frowned on.

Look at parts 9 and 18 on this diagram.


go to ebay and search for "dometic monitor" you will need to know the length of the current indicator


If its apart, replace the duck bill valves. they are cheap, and i could tell how the old ones were worn out.


I talked to the lady below a few years ago, she was knowledgeable about vht12s


Sonja Cariker

Marine Sanitation & Supply


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