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Old 11-06-2015, 01:16 PM   #1
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Puking Fresh Water

Hi All,

We recently picked up a 2003 National Dolphin LX 6342. The coach is clean and relatively free of problems. In fact, there's only one: The fresh water holding tank vent line pukes water, lots of it, when the coach is nose low, braking or turning right. This was checked by a repair facility and it was found that, yes, the thing pukes water as described. There are no leaks in the system so it holds water sitting still and level or nose up. We don't have a reference for how low it has to be to stop pouring water yet because we haven't puked enough out to get it below the 2/3 indicator light.

It looks like someone has changed the vent line because the one there now is 2" in diameter. I understand these are normally 3/8" or 1/2" at most. Also, the 2" line just dumps water on the top of the tank so it runs down the frame and out that way. The previous owner was an engineer and I suspect he may have had a 'better' idea than the factory on what the vent line should be.

I can always run with half a tank or less of water but what's the use of having 80 gallon capacity if you don't use it or half of it goes all over your car when towing.

There is one last fact that may or may not make a difference. This model Dolphin has two tanks connected together by a 1/2" or so dia. line.

Has anyone had similar experiences with this type of problem? If so, what did you do to correct it? I suspect we need to convert back to a smaller vent line to take care of this.

Thanks for any light anyone can shed.

Robert
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Old 11-06-2015, 03:16 PM   #2
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Had the same problem. Solved it by reducing the size using pieces of tubing til I got down to 3/8. Buy enough 3/8 tubing to go from that point under the mh
back to bumper, up the ladder til top rung, then a right angle, short tubing, another right angle, more tubing- maybe 2 foot. Then when you fill tank,
extra water will run right up the tubing and flow out the end. Shut off water .Go inside, flush toilet, which will use enough water to drop water level. Depending on your situation you may need some hose clamps to keep everything held together.


By filling tank and letting it overflow it flushes dust and stuff out. The tail end of tubing aims down and stays dry, No bees or mosquitoes 15 years.
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Old 11-06-2015, 04:28 PM   #3
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Originally Posted by anneb View Post
Had the same problem. Solved it by reducing the size using pieces of tubing til I got down to 3/8. Buy enough 3/8 tubing to go from that point under the mh
back to bumper, up the ladder til top rung, then a right angle, short tubing, another right angle, more tubing- maybe 2 foot. Then when you fill tank,
extra water will run right up the tubing and flow out the end. Shut off water .Go inside, flush toilet, which will use enough water to drop water level. Depending on your situation you may need some hose clamps to keep everything held together.


By filling tank and letting it overflow it flushes dust and stuff out. The tail end of tubing aims down and stays dry, No bees or mosquitoes 15 years.
That sounds like a solid solution, for sure. What model do you have? Did your RV have a 2" vent line you reduced?
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Old 11-07-2015, 08:03 AM   #4
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I have the same problem, I looked under the coach and the previous owner put a 2" ball valve in the line to fix the issue, now when it's full I close the valve and no more issues. I open it after a day or two of use.
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Old 11-07-2015, 10:30 AM   #5
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I have the same problem, I looked under the coach and the previous owner put a 2" ball valve in the line to fix the issue, now when it's full I close the valve and no more issues. I open it after a day or two of use.
Thanks for the information. It's obvious I'm not alone in this. I guess the 2" line is original although I can't imagine the factory thinking that is necessary.

Do you run the risk of rupturing a tank going up into the mountains or collapsing one coming back down with it closed? I guess you could leave it cracked to avoid such an issue. I wonder if it would work to run a long 1/8" or 1/4" drill through the ball valve when it's closed to allow it to vent a little?
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Old 11-07-2015, 11:01 AM   #6
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Quote:
Originally Posted by DDDonkey View Post
I have the same problem, I looked under the coach and the previous owner put a 2" ball valve in the line to fix the issue, now when it's full I close the valve and no more issues. I open it after a day or two of use.
DDDonkey
A fresh water tank vent only has to be big enough to let make up air into the tank as water is drawn out by the water pump.

A shut off valve in the vent line will prevent water loss while driving.

However if you have a shut off valve in the vent line it SHOULD BE OPEN anytime you use the water pump... to prevent an air lock and/or the possibility of tank damage due to "inward tank flex"... or "tank collapse".

Mel
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Old 11-07-2015, 11:36 AM   #7
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I have a 1999 TW and have the vent lines controlled by a valve, a piece of advice when using the water pump OR connected to city water make sure the vent lines are open so the tanks can vent. A failure of the pump check valve will allow city water to feed back into the water tanks and with vent closed you will explode the tanks.
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Old 11-07-2015, 10:37 PM   #8
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We have a 99 Dolphin with two tanks, total capacity 90 gallons. It has the original 1/2" vent line on each tank. When filling I have the rear slightly elevated to keep from siphoning water out the vent lines. Because the line between the two tanks is only 1/2" it takes a while to get both tanks full. When filling my tank I watch for water coming out the vent lines. As soon as I see water I stop the fill water. If not stopped quick enough water will be siphoned out the vent lines. Helps to have the rear higher then front. I wait for about 10 to 15 minutes and start filling again until I see water from the vent lines again. I continue the cycle until water comes out the vent lines as soon as I turn the water back on then I know both tanks are full. I always travel with full tanks for boondocking and know there is no place to fill up. I do lose a few gallons at first but not enough to worry about. While I say lines, I have only ever seen water come out of the left tank vent.
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Old 11-07-2015, 11:29 PM   #9
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I have to fill my tanks the same way. The equalizing line should be larger but that's not the way they did it so it does take several times to get it full.
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Old 11-08-2015, 05:42 PM   #10
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I have a 2001 Seabeeze. Made that mod maybe 5 years ago. Went to my friendly ace store with a scrap of tubing, and fiddled with their tubing set up till I got it down to a size that seemed sensible. Have had to replace the tubing coming from the right angle because of sun damage.


This is an open line, eltavation does not affect it.








on top of the ladder.
























































eyears ago. Have no idea of line at the tank. I just went to my good old Ace ha
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Old 11-08-2015, 07:39 PM   #11
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Thanks, Anneb. I climbed under the thing today and there's room between the back cap and the rear inside wall to run a line up and back down. At the corners, I could look all the way to the roof level. That would protect it from sun damage. I'm thinking that it could be looped up and over the rear window framing and back down the other side, no muss, no fuss, no sun damage.

Now, how hard is it to get into where the vent line is to start running a line back? How do you get in there? I have yet to figure that out. We had it looked at by an RV repair to see if the tank was damaged or anything and the tech described the existing 2 inch line but I couldn't get out of him how to get in there. Obviously, they want a sizable chunk of my wallet to do the work so information is hard to pry out of them.
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Old 11-08-2015, 09:37 PM   #12
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The tanks are behind the water panel in the wet bay. On my Dolphin to get to the tanks and water pump you take out about a dozen screws from the panel. The panel will come down, should be enough slack in the hoses to drop down out of your way.
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Old 11-08-2015, 11:00 PM   #13
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Quote:
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The tanks are behind the water panel in the wet bay. On my Dolphin to get to the tanks and water pump you take out about a dozen screws from the panel. The panel will come down, should be enough slack in the hoses to drop down out of your way.
That would be convenient. No need to mess with the hoses, just the vent line. Thanks.
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