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Old 08-05-2020, 17:18   #1
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Advice needed for installing new holding tank setup

First time dealing with any marine toilet plumbing. I am wanting to install a bulkhead mounted holding tank and a diverter valve for the option to discharge straight overboard. I just need a couple details ironed out before I order all the stuff.

Drawn a diagram attached to explain..

1. Can this join just be a standard Y connection and does it need any Ball valves to shut off certain pipes? Such as, when using the direct discharge option does the pipe from the tank need to be able to be shut off?

2. Do I need a vented loop in this line? The tank itself acts as the vented loop for the discharge pipe there but do I need a seperate one for the direct discharge?

Hope I explained well, thanks in advance!
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Old 08-05-2020, 17:30   #2
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Re: Advice needed for installing new holding tank setup

Kind of hard to understand the drawing so I’ll try to explain how mine is done.
The hose from the toilet goes directly to a three way valve that is attached directly to the thru hull, when the valve is open waste goes directly overboard, close it and the waste then goes into the tank.
Mine is an Apollo like this, but Groco also makes an excellent one.
https://www.defender.com/product.jsp...-1&id=3359523#

On edit it’s not actually open and closed, one way it’s open to the thru hull. The other way it’s open to the tank, there is no closed
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Old 08-05-2020, 17:52   #3
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Re: Advice needed for installing new holding tank setup

Sorry I'm a bit confused, if the tank is connected to the valve at the thru Hill how do you empty the tank?
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Old 08-05-2020, 18:20   #4
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Re: Advice needed for installing new holding tank setup

As you have drawn it, were the three way valve be set to the holding tank, the duckbill valve at the toilet fail open, and the flapper valve at the toilet bowl also fail open, the entire contents of the holding tank would drop back into the toilet bowl and overflow the toilet bowl. For lines full of s##t and paper bits, that is a real possibility. It would be a serious mess.
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Old 08-05-2020, 18:20   #5
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Re: Advice needed for installing new holding tank setup

What I'm getting from your diagram is that you are trying to use 1 thru hull for both tank and direct discharge.
My boat came from the factory with the option for direct discharge. They use separate thru hulls, macerator discharge (tank) is 1" while the one for the direct discharge is 1.5 " same as line from head.
A friend's French built boat has no macerator but a small tank mounted high that empties by gravity thru 1.5 " when you open the thru hull. Could you clarify what you want to do ?
I should add I've found the direct discharge unnecessary extra plumbing, and almost always utilize the macerator.
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Old 08-05-2020, 18:22   #6
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Re: Advice needed for installing new holding tank setup

The tank is one made to be mounted above the toilet, it has a pipe inside that prevents backflow.
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Old 08-05-2020, 18:27   #7
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Re: Advice needed for installing new holding tank setup

Ah yes, one thru hull. Can that not be done? I thought I would just be able to add some kind of junction in, but was unsure if it could be just a standard open type or another y valve.
And also yes, the tank is mounted high and drains by gravity.
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Old 08-05-2020, 19:00   #8
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Re: Advice needed for installing new holding tank setup

I did something similar a few years ago, actually the first project after I bought my current boat as the smell was horrendous. I had long permeated hoses leading to a holding tank under the stateroom berth, and then a long hose and macerator to pump it all back to the head. The macerator pump was broken... After removing that mess I was resolved to never have to deal with the risk of a macerator failing again.

I installed a new tank high on a shelf above the through hull, and the gravity drop works perfectly. The discharge hose from the head goes to the top of the holding tank. I also have a vent which works as a siphon break on the discharge side. I did include a vented loop for a siphon break on the head intake side. I don't have a Y valve for discharge, for sale of simplicity everything goes through the tank, and the valve on the through hull discharge hose suffices. I would have liked to include a valve on the discharge hose at the tank to keep the hose clear but had insufficient room so used high quality head hose and have had no issue with odors. I also installed a deck discharge hose, which is useful, as although we seldom pump out the tank from the deck, it is really handy to leave that open after emptying the tank to get good airflow through the tank via deck fill and vent. Apparently oxygen is helpful in promoting growth of bacteria that inhibit odor. In all of this I was helped immensely by Peggy Hall's excellent book on getting rid of boat odors.

Regarding the need for a vented loop on your direct discharge as drawn in your diagram, yes, I think you would. If the through hull were open and the Y valve set to direct discharge, something would be needed to prevent a potential siphon action. Good luck with your project!
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Old 08-05-2020, 19:10   #9
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Re: Advice needed for installing new holding tank setup

Ah yes! that's how our original tank was set up. It leaked and couldn't be pumped out so I also decided I never want to deal with that again, was not fun.

Awesome, thanks for that advice
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Old 08-05-2020, 19:41   #10
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Re: Advice needed for installing new holding tank setup

Ah yes, one thru hull. Can that not be done?

You should be able to use the same thru-hall for both direct discharge from the toilet and from the tank. But if you're gonna plumb the tank to either hold or flow through, why do you need to discharge directly from the toilet? When the thru-hull from the tank is open, you ARE flushing directly overboard.

And while I have the floor for a minute... Although the tank does have to be entirely above the boat's waterline for gravity discharge to work, mounting it entirely above the toilet isn't the best idea. Any marine toilet that's working anywhere close to factory specs--which means none of the rubber parts can be more than slightly worn--can lift bowl contents up to ("up to" is the operative phrase) 4'...but that's all, whatever doesn't make it all the way into the tank will run back down to the toilet and seep into the bowl.

I'll be glad to help you sort how to do this job if you'd like to give me a shout.

--Peggie
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Old 09-05-2020, 09:38   #11
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Re: Advice needed for installing new holding tank setup

I have installed a holding tank on my boat. I believe the vent is needed as it has to vent as you add waste to the tank and oxygen for the waste to promote growth and liquefy the waste. I have a separate input and output thru-hull. The tank is almost level with toilet and is a 15 gallon tank. I would be concerned about a gravity feed if for some reason the waste did not liquefy sufficiently. Of course if you have a 4" output it may not be and issue. The mistake I made is I used a tee pipe from the tank to the pump out hose and the macerator. The output seacock failed and I could not find a pump out station. With no way to empty the holding tank and no way to shut off the flow it was messy job. I strongly suggest you use a y valve diverter that allows you to shut off the flow to the seacock to assure the ability to work and repair any failures and avoid dealing with the crap. There may also be times you cannot dump into the ocean and must use the pump out
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Old 09-05-2020, 09:52   #12
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Re: Advice needed for installing new holding tank setup

For simplicity I just had mine so it all just went to/through the tank. Then the only necessary valve was the seacock. Just open the seacock to send it overboard!

Your diagram needs a pump out fitting on the tank. I just added a bronze T at the bottom tank outlet.
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Old 09-05-2020, 10:10   #13
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Re: Advice needed for installing new holding tank setup

For the vent question, where are the toilet and the "Y" at (1) in relation to the waterline?

If the toilet is well above the waterline then a vented loop is not a necessity, although most surveyors would tell you different.

If the "Y" can be above the waterline then the tank is your vented loop. Without pumping action, with the "Y" above the waterline it will always have air and thus a vent.

If the toilet and "Y" are both below the waterline then a vented loop in the direct discharge line should be installed.
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Old 09-05-2020, 10:26   #14
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Re: Advice needed for installing new holding tank setup

Quote:
Originally Posted by Jim Holland View Post
I did something similar a few years ago, actually the first project after I bought my current boat as the smell was horrendous. I had long permeated hoses leading to a holding tank under the stateroom berth, and then a long hose and macerator to pump it all back to the head. The macerator pump was broken... After removing that mess I was resolved to never have to deal with the risk of a macerator failing again.

I installed a new tank high on a shelf above the through hull, and the gravity drop works perfectly. The discharge hose from the head goes to the top of the holding tank. I also have a vent which works as a siphon break on the discharge side. I did include a vented loop for a siphon break on the head intake side. I don't have a Y valve for discharge, for sale of simplicity everything goes through the tank, and the valve on the through hull discharge hose suffices. I would have liked to include a valve on the discharge hose at the tank to keep the hose clear but had insufficient room so used high quality head hose and have had no issue with odors. I also installed a deck discharge hose, which is useful, as although we seldom pump out the tank from the deck, it is really handy to leave that open after emptying the tank to get good airflow through the tank via deck fill and vent. Apparently oxygen is helpful in promoting growth of bacteria that inhibit odor. In all of this I was helped immensely by Peggy Hall's excellent book on getting rid of boat odors.

Regarding the need for a vented loop on your direct discharge as drawn in your diagram, yes, I think you would. If the through hull were open and the Y valve set to direct discharge, something would be needed to prevent a potential siphon action. Good luck with your project!
If you want to keep the smell down, just bubble air through the holding tank. It is the anaerobic condition that produces the hydrogen sulfide. A trick you can pull is to push a small amount of air down the pump out line and then let the vent handle the exhaust. This also keeps the vent line open and clogs down. The air bubbled through the waste is exactly how a waste water plant works. Groco sells a product that does this.
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Old 09-05-2020, 10:36   #15
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Re: Advice needed for installing new holding tank setup

All tank vents have two main functions: to provide an escape for air displaced by incoming contents and provide a source of air to replace contents as they're pulled out.

When air displaced by incoming waste cannot escape out the vent the tank becomes pressurized, creating increasing back pressure that prevents the toilet from flushing.
Without a source of air to replace contents as they're being sucked out of the tank, the pump--pumpout or onboard pump--will pull a vacuum that'll prevent it from pulling out more than a gallon or two. A particularly strong pumpout can even implode a tank.

Creating an aerobic environment in a holding tank is an additional function that almost always requires some help from a tank product that stimulates bacterial activity.

I would be concerned about a gravity feed if for some reason the waste did not liquefy sufficiently.

You needn't worry about how quickly waste dissolves in the tank..solid waste is at least 75% water, so it dissolves very quickly. And so does quick-dissolve TP...it turns to "snow" in as little as an hour.

I strongly suggest you use a y valve diverter that allows you to shut off the flow to the seacock to assure the ability to work and repair any failures and avoid dealing with the crap.

A good idea...but also make sure it's rarely needed by doing a bit of preventive maintenance which can be done when it's convenient...failures never happen when it is.

--Peggie
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