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Old 21-05-2019, 14:42   #1
kcj
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Holding tank vent

In the process of redoing plumbing on a 2003 lagoon cat...I have come to find the holding tank vent fitting appears to have a dip tube to the bottom of the tank.

This Does not make sense to me...what is the logic? Or Should I try to remove the tube?

Thanks in advance.
Cheers
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Old 21-05-2019, 14:58   #2
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Re: Holding tank vent

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...holding tank vent fitting appears to have a dip tube to the bottom of the tank. This Does not make sense to me...Should I try to remove the tube?
Me neither, the vent's to allow air/gas to escape out of the top as the tank fills; I've fitted/plumbed four holding tanks over the years and the vent goes at/near the high point of the tank opening directly into the tank. However, before chopping it off, make doubly sure that you're not confusing a 'vent' outlet, with perhaps an outlet for a deck pump-out fitting; has some 'engineer' in the past incorrectly connected the two?
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Old 21-05-2019, 16:06   #3
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Re: Holding tank vent

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Originally Posted by kcj View Post
In the process of redoing plumbing on a 2003 lagoon cat...I have come to find the holding tank vent fitting appears to have a dip tube to the bottom of the tank.

This Does not make sense to me...what is the logic? Or Should I try to remove the tube?

Thanks in advance.
Cheers
John
What you describe is not at all a rational installation, the vent needs to come off the top of the tank.

If this is a factory install, you almost SURELY are misunderstanding what you are seeing. I am not a fan of Lagoon fit and finish, but they didn't build it the way you describe. If it was made the way you describe, every time you pumped waste into the tank it would overflow out the vent fitting.

Are you SURE you are not mistaking the pumpout fitting for the vent???
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Old 21-05-2019, 17:20   #4
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Re: Holding tank vent

Thanks for insights... I will test further in the am, but itís certainly not the fill or pump out... and my gut, based on the way hoses were run, is that it was a factory install.... maybe the tube I saw is opened at the top as well as the bottom.... more to follow...
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Old 21-05-2019, 17:26   #5
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Holding tank vent

Only reason I could see a dip tube is if an owner had installed a bubbler to pump air into the waste to help prevent smells.
But that would require a separate vent.

Want is the diameter of this dip tube?
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Old 21-05-2019, 17:42   #6
kcj
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Re: Holding tank vent

I was thinking it could be a mod... it looks like a .5Ē hose coming down from the vent fitting... Iíll check what the two pump out fittings look like as well...(deck and overboard, they are 1.5Ē)

Btw factory vent setup is pretty funky... .5Ē hose, 20í mostly horizontal run to strainer , that then ďdrainsĒ down two feet to thru Hull just above waterline...but I have no clear idea on how to improve it...
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Old 21-05-2019, 17:47   #7
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Re: Holding tank vent

Ideal vent is large and straight, and as short as possible.
If you could have two one on each side of the hull, that would be ideal, but possibly not worth it.
Iíve just accepted that the contents are going to stink, period.
It didnít on any of my RVís, but they had a large vent that ran straight up through the roof, like a house does, plus we always put chemicals to treat the waste in.
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Old 21-05-2019, 18:12   #8
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Re: Holding tank vent

Wait...

the outboard fitting for the holding tank vent is 20 feet away from the tank and down near the waterline???? And what do you mean by a ďStrainerĒ? Why should there be a strainer in a vent line?
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Old 21-05-2019, 18:26   #9
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Re: Holding tank vent

Just buy this book:


https://shop.sailboatowners.com/prod...+of+Boat+Odors
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Old 21-05-2019, 18:32   #10
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Re: Holding tank vent

Itís a French boat.........????? I love my lagoon, but this part is a little odd... itís in the drawings that way...both port and starboard, or should I say babord and tribord... and Iím pretty sure it is not the way Peggy would design it...holding tank is under floorboards amidship. Vent runs aft to engine room where the sea type Strainer and thruhull are... not keen on putting a hole in the hull amidships...
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Old 21-05-2019, 18:43   #11
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Re: Holding tank vent

That set-up would not let the tank drain...... have to have air above to drain. follow the hoses.
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Old 21-05-2019, 19:21   #12
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Re: Holding tank vent

In the process of redoing plumbing on a 2003 lagoon cat...I have come to find the holding tank vent fitting appears to have a dip tube to the bottom of the tank.

That's not the vent...it's the tank discharge fitting. Putting it on the top of the tank with a diptube to the bottom inside the tank instead of putting the discharge AT the bottom of the tank isn't uncommon because it eliminates standing sewage in the tank discharge line. And I cannot believe that NONE of you who replied had ever seen that before or even knew what it was!


Now...as for the tank VENT:

Although you'll often find the vent fitting on the end or side of the of the tank AT the top of it, the vent fitting really belongs ON the top of the tank too, because a vent fitting on the end or side lowers the usable capacity to the bottom of the vent fitting.

--Peggie
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Old 22-05-2019, 07:13   #13
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Re: Holding tank vent

Some followup pix... First is the top of tank.. Vent fitting in question is on lower right. Diagonal pvc is input from head, fitting in lower left is overboard discharge pickup.

Second pix is from inspection port,inside tank, facing vent. Down tube in question is on left, white tubes on right are from tank level sensors

Third pix is rotated toward sensors.. You can see both down tubes

Also found a waste system diagram on the vetus site which mirrors what I have re the strainer setup .. But it is silent on the vent tube issue. And they are vetus fittings.

So just what am I looking at on the left of second pix?

Thanks
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Old 22-05-2019, 10:21   #14
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Re: Holding tank vent

I think I've got it...the two larger tubes in the third photo are tank discharge diptube on the left...the inlet from the toilet is on the right ...and the vent fitting is the smaller fitting that's just poking out of the top of the tank on the right

I have NO idea why the diptube doesn't go all the way to the bottom of the tank or what that thing under it is...nor why there'd be a tube on the inlet fitting or what the thing under IT is. The vent fitting is the only one that begins to make any sense, and without a more detailed look at it, I'm not even sure that it does! Nor do I have the foggiest idea what the thing that looks like a large diameter pipe at the far right edge of your photo is.

Looking at your first photo, I see the inspection port and another threaded port that I'm almost certain is some kind of tank level indicator. I can't match up anything in the second photo with what I see in the third one...UNLESS what I thought was the inlet piping is the sender for the tank level indicator. If so, there has to be another fitting on the top of the tank that doesn't have a tube inside the tank. I'm totally baffled by the collection of fittings and pvc pipe. I'm guessing that the smaller clear hoses at the bottom edge have nothing to do with the sanitation plumbing

I can definitely see that the tank is in serious need of a thorough cleaning out! What's it made of--metal? Fiberglass? Doesn't look like plastic..?

I'm kinda thinking that the best approach would be to remove everything that's in the tank and replace it all with new fittings--including a diptube on the discharge--done correctly. I'll be glad to help you with that.

--Peggie
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Old 22-05-2019, 10:28   #15
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Holding tank vent

Quote:
Originally Posted by peghall View Post
That's not the vent...it's the tank discharge fitting. Putting it on the top of the tank with a diptube to the bottom inside the tank instead of putting the discharge AT the bottom of the tank isn't uncommon because it eliminates standing sewage in the tank discharge line. And I cannot believe that NONE of you who replied had ever seen that before or even knew what it was


Except he said it was .5Ē in diameter, not 1.5Ē, so itís not a discharge dip tube, I guessed maybe it was for air injection, because I couldnít come up with any other reason it may be there.

Just from appearances, it looks to be an aluminum tank, if so and I was fixing to redo everything, I believe Iíd start with a new plastic tank and forego the cleaning fun.
And Iíd go with a Solo tank monitor on a plastic tank and not with floats.
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