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Vented loop vent confusion/waste system sanity check

6742 Views 26 Replies 13 Participants Last post by svHyLyte, Aug 8, 2014

UltimateWalrus

Discussion Starter · Aug 6, 2014

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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svHyLyte

· #21 · Aug 8, 2014

Stu Jackson said:
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.

Ah... Evidently you didn't notice/understand the symbology. In the given illustration there is no "macerator pump". There is only a hand operated Whale Gusher diaphragm pump to direct/pump waste from the holding tank to the through hull. With a good enzyme "digester" additive to the holding tank, the Whale Gusher is quite good at moving the liquified effluent out of the boat. This arrangement worked well/reliably on our former yacht from 1976 until early 2002 and has been working equally well on our current yacht since 2002 through the present. But heck. What do I know, eh?

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mitiempo

· #22 · Aug 8, 2014

RichH said:
Its very simple, If the vent valve on the water inlet to the head allows a greater volume of air than the pump can move water, you will only pump air and not much water to the head/bowl. The air flow through-put of the that vent valve must be sized/selected so that the volumetric flow of air does not reduce what the hydraulic static head requirement to pump water to the bowl. Usually a small fixed diameter orfice is added to the vent valve to control the amount of air flow and still allow enough flow to 'break' any suction that would allow siphoning of water into the boat if that bowl is below the waterline.
Simple hydrostatics.

There should NOT be a vented loop between the inlet through hull and pump on a Jabsco type head. The pump isn't strong enough to pull with one, especially after a bit of wear. That is why Jabsco recommends the ant-siphon vented loop be installed between the pump and the back of the bowl. The small section of hose that ships with a Jabsco isn't even marine grade hose and needs to be replaced during installation. This places the vented loop on the output side of the pump and it works without and suction problems.

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svHyLyte

· #23 · Aug 8, 2014 (Edited)

mitiempo said:
There should NOT be a vented loop between the inlet through hull and pump on a Jabsco type head. The pump isn't strong enough to pull with one, especially after a bit of wear. That is why Jabsco recommends the ant-siphon vented loop be installed between the pump and the back of the bowl. The small section of hose that ships with a Jabsco isn't even marine grade hose and needs to be replaced during installation. This places the vented loop on the output side of the pump and it works without and suction problems.

Ah... Well.. Brian, you're almost correct.

One does not want an uncontrolled vent if one's pump is on the "suction" side of a vented loop. But, with few exceptions, one does want/need a vented loop in the raw water feed line if one's toilet will ever be below one's water line for any period. To deal with the issue of loosing "prime" when one needs use the pump, there are two alternatives for the suction side of the pump. One complicated. One simple.

The "complicated" approach is to install an electric shut-off valve in the vent line such as the Jabsco 12v "solenoid" vent control, Jabsco part number 37068-0000, which is activated by a small push button near the head when one needs "flush" (i.e. pump) the head (the method we use in our aft head which is fitted with an electric raw water and maserator pump). The second approach (the one we use on our forward, hand operated toilet) is a small fitting on the bulkhead behind the toilet that the vent line from the top of the raw water intake loop is connect to. A half turn "closes" the vent, allowing the pump to work quite nicely. Once the bowel is cleared, a half turn of the valve in the opposite direction opens the vent. With this, the forward toilet remains free of the hazard of siphoning. And, the "drill" isn't hard to learn. Even our daughter learned the routine when she was only four years old.

FWIW...

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mitiempo

· #24 · Aug 8, 2014

Actually I am correct. Here is a link to Jabsco's instructions for their most popular manual head: http://ec1.images-amazon.com/media/i3d/01/A/20/00/00/0/0000001220.pdf

And here is the pertinent section:

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Capt Len

· #25 · Aug 8, 2014 (Edited)

I gang the vent line together with the black water discharge vent using a manifold of 1/8 copper L's and T's . the flushing keeps the lines clear and all drains to the toilet bowl.(no dribbles down the plumbing) Thirty years ago I sent wooden boat mag an article showing what Brian just said .After asking the marine toilet industry they said 'Thanks but no merit' Brydon Boy immediately changed their literature so somebody rethought the issue. As we are doing again in this thread.

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RichH

· #26 · Aug 8, 2014

Most definitely this the absolute SAFEST way to plumb an onboard toilet

mitiempo said:
Actually I am correct. Here is a link to Jabsco's instructions for their most popular manual head: http://ec1.images-amazon.com/media/i3d/01/A/20/00/00/0/0000001220.pdf

And here is the pertinent section:

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svHyLyte

· #27 · Aug 8, 2014 (Edited)

mitiempo said:
Actually I am correct. Here is a link to Jabsco's instructions for their most popular manual head: http://ec1.images-amazon.com/media/i3d/01/A/20/00/00/0/0000001220.pdf

And here is the pertinent section:

Yup. Which goes to show there is more than one way to skin a cat, eh? (And I have added an addendum to my earlier comment to clarify my intent.)

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