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Old 02-08-2020, 03:35   #1
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Vented loop necessary?

Hello all! First post on this great forum! I'm planning to convert my boat's head to a fresh water flush and to temove the overboard pump-out. I'd be running an intake line to the toilet from a new separate water tank">fresh water tank, and running the black water line to the existing holding tank, which has a deck pump-out fitting. All components are below the waterline. The question is: is there any need for vented loops in this arrangement?
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Old 02-08-2020, 03:47   #2
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Re: Vented loop necessary?

If there is no path from the ocean to your head, then no. For sanitary purposes I assume you have check valves to stop back flows.
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Old 02-08-2020, 03:57   #3
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Re: Vented loop necessary?

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If there is no path from the ocean to your head, then no. For sanitary purposes I assume you have check valves to stop back flows.
^^^

This... unless the freshwater supply tank is higher than the top of the loo.... in which case you would need some kind of syphon break, between the pump and the bowl.
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Old 02-08-2020, 04:45   #4
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Re: Vented loop necessary?

You need a siphon break at the head itself, check valves won’t suffice, you need an air gap.
Assumption is your buying a fresh water flush head? If so then it will be safe and a lot easier than installing a tank just for the head.
If your refilling the tank from the head without a siphon break, then it’s not any safer than connecting to your regular water tank.

My Raritan head has a simple siphon break right at the bowl, simple small thing.
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Old 02-08-2020, 04:55   #5
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Re: Vented loop necessary?

The current plumbing has a loop without a vent in the discharge hose, so I'll probably keep that, and put a check valve in the intake hose. Thanks guys!
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Old 02-08-2020, 05:32   #6
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Re: Vented loop necessary?

The OP indicated a new separate flush water tank. That solves the back flow problems, although he needs to be certain not to connect it to his potable system.
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Old 02-08-2020, 05:38   #7
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Re: Vented loop necessary?

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You need a siphon break at the head itself, check valves wonít suffice, you need an air gap.
Assumption is your buying a fresh water flush head? If so then it will be safe and a lot easier than installing a tank just for the head.
If your refilling the tank from the head without a siphon break, then itís not any safer than connecting to your regular water tank.

My Raritan head has a simple siphon break right at the bowl, simple small thing.

I've got a Johnson Pump Aqua-T head. I figured that with a closed system, if everything goes wrong, the most water (and waste...) that could end up in the bilge is the total volume of the fresh water tank and the holding tank, since there would be no through-hulls. I suppose there is a risk that the fresh water would continue to flow uncontrollably through the pump to the bowl, and hence to the bilge until the tank runs dry? And this is prevented with a syphon break?
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Old 02-08-2020, 05:44   #8
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Re: Vented loop necessary?

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The OP indicated a new separate flush water tank. That solves the back flow problems, although he needs to be certain not to connect it to his potable system.

Exactly. I intend to keep it completely separate; tank, filler, breather.
Now, I do mostly day sails, and when I do overnights, they're places that have some form of toilet facilities. At home I have pump-out and fresh water available. The boat doesn't have a lot of space for a second tank, so the volumes are really modest. My holding tank is only 25 liters.
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Old 02-08-2020, 09:01   #9
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Re: Vented loop necessary?

If you want to be able to flush your sea water toilet with fresh water, there's a much simpler way to do that safely (no risk to the potable water supply) that works on all boats that have the toilet and head sink on the same side of the keel: reroute the toilet intake line to tee it into the head sink drain line. To flush, close the sink drain seacock (assuming your sink drain thru-hull is below waterline)...if the thru-hull is above waterline, install a shutoff valve in the drain or use a tee that includes a shutoff valve, fill the sink with clean fresh water (NEVER use gray water!)...flush the toilet.


The beauty of this is, you can have it both ways if--as is true of most sailboats--your head sink drain thru-hull is below waterline..you can conserve your fresh water by continuing to use sea water to flush, switching to sink water only to rinse all the sea water out of the entire system--intake line, pump, channel in the rim of the bowl AND the discharge line--last thing before leaving the boat or as often as you think necessary. To do that, the tee in the drain line needs to be below waterline as close to the seacock as possible. You'd still need the vented loop in the toilet INTAKE, installed between the pump and the bowl.



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Old 02-08-2020, 15:44   #10
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Re: Vented loop necessary?

Iím still a bit confused about WHY youíd want to flush with fresh water. What is the advantage?
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Old 02-08-2020, 17:29   #11
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Re: Vented loop necessary?

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Iím still a bit confused about WHY youíd want to flush with fresh water. What is the advantage?
Less smell

Some more inland places I have sailed the rinse smelled worse than what I was flushing!
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Old 02-08-2020, 19:49   #12
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Re: Vented loop necessary?

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Less smell

Some more inland places I have sailed the rinse smelled worse than what I was flushing!
Ah... right. Not a problem around here, thank goodness, but yes, I can see the logic now, thank you.
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