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Discussion Starter #1
Hi All...

If a toilet discharge is piped directly to a holding tank, is a vented loop necessary? If not, what keeps the tank from spilling or otherwise backing into the toilet, or even into the discharge tube?

Currently I have the toilet discharge going to a diverter valve, then to either the seacock or the tank. The seacock is never used, and the diverter valve is never changed, always leading to the tank. I could take it out, but the hose from the valve to the tank is in place, so I don't want to fool with it.

When I replace the toilet, I plan to just run the discharge to the existing valve. I am trying to figure out of I need a vented loop.

Thanks...
 

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Discussion Starter #2
But if I did want to remove the diverter valve, could I join a new section of discharge hose to the existing one that goes to the tank? How?
 

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STARBOARD!!
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If the diverter valve is high enough above both the holding tank and the toilet; the sloshing under normal sailing conditions should not cause backflow into the toilet. In my opinion; you should keep the option of overboard discharge; unless you are located in a landlocked area (lake or similar) where discharge would always be considered illegal. To answer your quesion about what would keep the sewage in the tank; it's the joker valve on the toilet. The joker valve is a 1-way valve on the exit side of the toilet; prevents backflow of sewage into the toilet bowl. You can't trust it as a prevention from flooding (via the seacock); as there should always be a vented loop between the seacock and the y-valve; and a vented loop between the bowl and the hand pump on the water inlet line.

To plumb the existing line directly to the holding tank; you would need a hose-barb union (hose barbs on both ends) or equivalent of the correct diameter.
 

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Telstar 28
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The holding tank input line is usually plumbed at the top of the tank... so that incoming waste doesn't have to force its way in against the pressure of the existing contents of the holding tank. It is pretty unlikely for a holding tank to every siphon back in to a head for this reason....unless you've massively overfilled it. Also, the tank's vent line acts as a siphon break.

My preferred way of plumbing a head is to have the head discharge directly into the tank. Then to have the pumpout line from the tank equipped with a diverter valve, one side of which goes up to the deck pumpout fitting and the other of which goes to a diaphragm pump or macerator pump and then to the seacock and through-hull.

This setup minimizes the plumbing but maximizes the flexibility of the system. Some say you lose capability, but in reality, you don't, since anywhere you could have discharged the head directly overboard, you can dump the tank out.

With the diverter valve, it is unlikely that you need a vented loop in the discharge line, since the head can't siphon through the diverter valve.
Hi All...

If a toilet discharge is piped directly to a holding tank, is a vented loop necessary? If not, what keeps the tank from spilling or otherwise backing into the toilet, or even into the discharge tube?

Currently I have the toilet discharge going to a diverter valve, then to either the seacock or the tank. The seacock is never used, and the diverter valve is never changed, always leading to the tank. I could take it out, but the hose from the valve to the tank is in place, so I don't want to fool with it.

When I replace the toilet, I plan to just run the discharge to the existing valve. I am trying to figure out of I need a vented loop.

Thanks...
 

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I agree with "Saillingdog's" pumbing plan and my system follows his description, but without the diverter valve at the effluent from the holding tank. A simple "T" plumbed at the effluent leading to the macerator with through-hull seacock at one side and to the deck pump out at the other will suffice. When the macerator seacock is closed then all suction will apply to the tank from the deck pump out & when the deck plate is closed all suction will be applied from the macerator pump. I've used this simple plan for tewnty years without a problem. 'take care and jopy, Aythya crew
 

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Discussion Starter #6
I like the concept SD described as well. I suppose that it is more capable then the diverter valve right after the toilet, because the was SD described it, the tank can be emptied, which is not true if I leave it set up as is.

In my case, the seacock is right next to the toilet and the tank is well up forward, about 8 or 10 feet. To do that I would either need to run an additional hose back from the tank area to the seacock or add a new seacock more forward.

Realistically, I don't ever see myself discharging through the seacock, either directly from the toilet or from the tank, so I am not inclined to run the new hose or install a new seacock, at least not this season.

Since I'll never open the seacock, I am thinking I should wire tie it shut, wire tie the diverter valve shut and just use the diverter valve as a coupling. In the future I could easily add a vented loop between the toilet and the diverter valve, or replumb it as suggested above, if I ever think I'll need to discharge.

So I guess I'll add a vented loop between the intake pump and the bowl, but nowhere else.

Does this make sense?
 
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