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Old 16-12-2009, 20:05   #1
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Vented Loops on Non-Overboard Sytems

Hello,
For starters, I ran across this board while doing a search on the use of vented loops and believe my question might be able to be answered here.
This past summer I bought a small cruiser, 29' Baja that came with a Jabsco manual head, which I just bought a conversion kit to convert it over to the newer quiet flush electric system. The holding tank on my boat only accepts from the head, nothing else goes into it. It does not have overboard discharge feature, just the plain dock side pump out. (I'm on a small inland lake). Both the head and holding tank are mounted on the same level. My boat has a vented loop, which I don't understand why, since it does not discharge overboard. I'd like to remove it to do away with the slight odor in the cabin, plus can eliminate over 1/2 of the 1 1/2" hose. I think it would be more efficient with out the additional height of the outlet hose going to and from the vented loop that would retain the waste. I emailed Jabsco, but they only referred me to their website Q & A's, which (as with every other site I found) only considers waste systems with overboard discharge/thru hull fittings and relation to the water level, which I don't believe is a factor in my situation

Thanks in advance for any replies.

Jerry
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Old 16-12-2009, 20:10   #2
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You have no need for a vented loop. Just be sure you're dumping into the top of the tank with no way for waste to siphon back to the head.
The only reason to have the loop is to prevent the sea from attempting to even up it's level inside and outside of the boat.
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Old 16-12-2009, 20:21   #3
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Yes, the hose is connected at the top/side of the holding tank. Thanks for the quick reply. By eliminating the loop, I can flip the tank around so the outlet at the bottom is at a slight lower elevation than it is currently is making for a more complete pumpout, and also puts the inlet connect against the adjoining wall to the head for a much shorter lenght of hose, approx just 3' total vs. the current 9'.

I wonder why there is one there. Just a standard building procedure?
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Old 16-12-2009, 21:02   #4
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Where does the inlet water come from?
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Old 16-12-2009, 21:38   #5
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Where does the inlet water come from?
From the freshwater tank. The conversion kit comes with a solenoid/vacuum break that is installed in the supply line just ahead of the toilet to prevent any type of contamination. I guess that's possible?
However, the factory setup with the manual pump was plumbed to the fresh water tank w/o any type of device on the inlet side. Not saying that's right, just how it was/is.

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Old 16-12-2009, 21:40   #6
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Originally Posted by US1Fountain View Post
Hello,
For starters, I ran across this board while doing a search on the use of vented loops and believe my question might be able to be answered here.
This past summer I bought a small cruiser, 29' Baja that came with a Jabsco manual head, which I just bought a conversion kit to convert it over to the newer quiet flush electric system. The holding tank on my boat only accepts from the head, nothing else goes into it. It does not have overboard discharge feature, just the plain dock side pump out. (I'm on a small inland lake). Both the head and holding tank are mounted on the same level. My boat has a vented loop, which I don't understand why, since it does not discharge overboard. I'd like to remove it to do away with the slight odor in the cabin, plus can eliminate over 1/2 of the 1 1/2" hose. I think it would be more efficient with out the additional height of the outlet hose going to and from the vented loop that would retain the waste. I emailed Jabsco, but they only referred me to their website Q & A's, which (as with every other site I found) only considers waste systems with overboard discharge/thru hull fittings and relation to the water level, which I don't believe is a factor in my situation

Thanks in advance for any replies.

Jerry

Look at page 4 in the below link, it shows systems that only go into the holding tank, and explains when they believe it is required to have a vent and when it is optional.

http://www.jabsco.com/files/itemdoc142681.pdf

Baja is a power boat correct?

I agree with Sailmonkey, I don't see the need for a vented loop in the outlet on this system. Your valves would have to have failed and you would have to be driving hard enough to splash enough sewage out of the top of the tank back down hose to the head to fill it enough to spill/overflow the head. Sounds improbable, and not a sinking issue.

I think Ex-Calif is insinuating that you need a vented loop on the intake line if your head is below the waterline.
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Old 16-12-2009, 21:58   #7
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Yes that's what I was asking about.

Jabso uses pretty strong language for option 3. I just wonder if there are holing tanks that have a drop pipe into the tank. They seem pretty confident a tank above the discharge elbow will siphon back.
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Old 16-12-2009, 22:01   #8
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Yes. Baja made a 29 'and 34' cruiser model in mid 90's before discontinuing the cruiser line and concentrating on the sport boat line.

As I understand the link you included, it states I must use a vented loop since the top of the holding tank is always above the discharge elbow, which is how mine is. I agree that I don't think I need one since it isn't a sinking issue, but everything I read suggests I do. Maybe if as you say the valves have failed and the tank is full, then I can see it being a case of some back flow into the bowel, but then even if it had a vented loop, that is still a possiblity if the tank was full to the max to where the hose was holding waste, just short of flowing out the vent. I venture to say this to never be the case. Small lake and the pumpout station is right across from my slip, so not an issue to do.

I assume for all practical purposes, waterline is not a factor in my situation?

Thanks
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Old 16-12-2009, 22:07   #9
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Yes that's what I was asking about.

Jabso uses pretty strong language for option 3. I just wonder if there are holing tanks that have a drop pipe into the tank. They seem pretty confident a tank above the discharge elbow will siphon back.
That does sound like a high possibilty. However in my case, I don't believe there is an inside drop pipe. The elbow/hose barb just screws into the side of the tank. I'll take a closer look tomorrow to be sure.
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Old 16-12-2009, 22:11   #10
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Maybe if as you say the valves have failed and the tank is full, then I can see it being a case of some back flow into the bowel...

It's possible but I'm pretty sure you'd have to be sitting on the bowl for that to happen.

(Sorry - couldn't resist)

PS - this is definitely not a sinking issue. Might be a stinking issue...
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Old 18-12-2009, 16:41   #11
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Too many vowels in my bowels.

Alrighty then, the loop is coming out along with the extra lenght of hose.
Thanks all
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Old 18-12-2009, 18:44   #12
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I personally like a system where the outflow goes into the top of the tank. As long as you don't fill it past capacity it can't back siphon. Even then it would be nasty, but not sink the boat if your holding tank doesn't empty overboard.

I learned the hard why on my first boat why it's needed when the head out is attached lower on the holding tank with no vented loop.

My favorite system is installed in one of my boats: Head empties into top of holding tank with no siphon loop. Tank gravity empties simply by opening the seacock.
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