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Vented loop vent confusion/waste system sanity check

6742 Views 26 Replies 13 Participants Last post by  svHyLyte
I could use advice from people who know about holding tank systems.

I'm aiming to install a new holding tank system from scratch. For whatever reason my 1976 Ericson 29 does not have one and does not appear to ever have had one... just two thru-hulls, one for intake and one for output.

I've done hours and hours of research and come up with this diagram of the waste system I intend to implement:


I think it should be OK, provided I can get everything to fit together and muster up the courage to buy 100's of dollars of components and drill a couple above-waterline holes through my hull. Though if anyone has any feedback or suggestions on how I am approaching this I'd be glad to hear it.

My biggest confusion right now is coming from how I'm supposed to connect the vented loop to the vent line. I'm planning on trying to use 1.5" sanitation hose for everything (including the vent line, which as I understand it, is better off thick to allow the holding tank more oxygen). However, the biggest hose any vented loop will accept on its vent is 1/2" as far as I can find, and the cheap one I would prefer to buy, has a measly 1/4" port with its adapter.

On top of that, it states that the valve has to be removed to insert the adapter. I researched and found that if you attach to a vent line, the loops are more reliable without the valve anyway. This is all fine and good, except that as far as I can tell there will now be sewage splashing up into the vent line every time I pump the head. This means, if I don't want to deal with terrible smells, I have to somehow find a 1/4" ID marine sanitation hose (which I can't find anywhere), AND adapt it to a tee connector on the 1-1/2" marine sanitation hose I plan on using for the vent.

I cannot find an adaptor anywhere that will let me adapt a 1/4" hose to 1 1/2", much less one designed for sewage. I can't even find a combination of adapters that would work; the closest I could get is this tee connector, and it's still three times too big.

Did part manufacturers as a whole really overlook a standard, widespread head configuration, or am I just blind, crazy and overthinking things (I suspect the latter)?
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Boy, are you ever overthinking this.

And reinventing the wheel.

Try this:

Selecting a Sanitation System | West Marine

I dislike their final solution in the big picture at the bottom, because everything has to go to the holding tank.

Our system is simpler: either into holding tank or overboard. Pump out or macerator pump from tank. Simple.

Vented loop between the head hand pump and the bowl, NOT on the intake line from the seacock to the head hand pump.

Vented loop is optional between the head output and the tank, we don't have one, been working fine for 16 years.

Treat the holding tank with Odorlos - Google it.
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GOOD DIAGRAM !!!!
Some advocate a 'small' vented loop (the vent valve on the vented loop being 'small') on the inlet to the toilet head line; but, that has to be carefully and accurately sized so that the vacuum generated by the heads manual water pump exceeds the in-rush air leakage of the vented loop - this is to prevent flooding though the toilet in case the toilets dry/wet valve is faulty; if faulty the head will flood into the boat especially if the top of the toilet bowl is below the waterline. The inlet line vented loop height is dependent on how far below the static waterline the toilet is mounted and how far the top of the vented loop is above the static waterline when the boat is well heeled over.
It's actually a rather poor diagram.

The macerator should have its own thru hull, because the outlet of the macerator is much smaller than the head outlet.

Therefore, that Y valve isn't needed.

The pump out should have its own connection to the tank.

So, only one Y valve is needed on the head outlet: overboard or to the tank. And you could do it with a simpler ball valve.

This discussion about vented loops is wrong, unless I'm reading it wrong. It's simple: vented loop between the pump on the head and the head bowl. It's a 3/4 inch line with a 3/4" vented loop, nothing to "carefully size" at all. This is required basic stuff and available in ALL head manufacturer's literature for head installation. The heads come with a short piece of white hose between the pump and the bowl. Replace it.
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