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Old 04-26-2018, 06:12 PM   #1
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Fresh water tank self draining?

I have a 2015 FR33. This has happened once before and I know it has been discussed but i've been unable to find the thread. Filling my fresh water tank until water comes out what i believe is the overflow. Problem is it siphons the tank dry. It doesn't happen every time so i'm having a difficult time figuring out how to stop it
My TT had an air vent over the fill inlet and would allow the pressure to equalize. This is draining from a tube next to my low point drains.
Any Ideas?
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Old 04-26-2018, 06:18 PM   #2
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Either try to adjust the over flow tube or many will put a 1/4 turn valve on the tube to stop the siphon. My parents Georgetown would empty out by just the suction from the wind during drivng. It would start the siphon action and they'd have no water by the time they got to where ever...
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Old 04-26-2018, 06:34 PM   #3
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I fill the onboard water tank until the water comes out the overflow pipe.
I installed this in-line tap to stop the water from siphoning out.

https://www.homedepot.com/p/LEGEND-V...-600/203581043

JUST REMEMBER.....TO OPEN THE TAP BEFORE USING THE PUMP!
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Old 04-26-2018, 06:45 PM   #4
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Originally Posted by kenandterry View Post
I fill the onboard water tank until the water comes out the overflow pipe.
I installed this in-line tap to stop the water from siphoning out.

https://www.homedepot.com/p/LEGEND-V...-600/203581043

JUST REMEMBER.....TO OPEN THE TAP BEFORE USING THE PUMP!
Hmm yes.. And if you plug the vent tube, unplug before filling... The Old man popped some supports and blew out a wall by filling the tank and not allowing air to escape... Then, yes, he suck the tank into itself a bit with the pump.. Luckily my RV repair services were cheap!
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Old 04-27-2018, 07:30 AM   #5
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Thanks for all the responses I plan on putting in a valve. In regards to that is there any reason that compartment is walled of with a port in it? My hand barely fits through it and i can't see anything.
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Old 04-27-2018, 07:35 AM   #6
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Originally Posted by Leerich View Post

Thanks for all the responses I plan on putting in a valve. In regards to that is there any reason that compartment is walled of with a port in it? My hand barely fits through it and i can't see anything.
I would screw the valve into the vent hole right next to the fill cap so it is visible when you fill it.
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Old 04-27-2018, 07:57 AM   #7
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putting a shut off valve on the overflow/breather tube is really a short term fix (I did this for a while) (my overflow/breather tube after a time cracked at the top and I no longer have this siphon effect problem). You must stop the siphoning effect of the overflow/breather tube. The siphoning effect happens because it is a 'closed system' tube/tank suction. You must open up the area to the tank and put a 'breather hole' going higher than the tank in order to 'break' the suction effect. By always 'closing off the bottom' of the overflow/breather tube with a full tank of water..... The fresh water tank is TOO FULL and bulging.... This will put a lot of stress on the supports and fresh water tanks on towables can 'fall out' due to the weight and bulge..... I know that you have a FR33 and the water tank is most likely supported inside the unit (and will not 'fall out') as some do on towables. But the bulging tank will give you some big problems down the road. As I said, when I 'capped' the 'overflow/breather on mine, there was a lot of pressure on the tank/drain tube and the tube ended up cracking/coming loose at the glue point area.
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Old 04-27-2018, 08:11 AM   #8
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Leering....

I originally removed the wall you are talking about and it allowed me to view all the workings located behind. I found the sensors to monitor the fresh water tank levels, the “Arctic Pack” heating pad, the on board water pump and it’s in-line fuse, the winterzation by pass taps, etc. Only the smallest access was available through the screw in access door. It was nice to have a clear look,at everything in behind. The plastic wall is simply there to protect all the items listed above from any objects you store in that compartment.

I decided where to install my in-line tap, and then cut out a small section of the wall to have access to the tap when the wall was reinstalled.
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Old 04-27-2018, 08:33 AM   #9
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Quote:
Originally Posted by Leerich View Post
I have a 2015 FR33. This has happened once before and I know it has been discussed but i've been unable to find the thread. Filling my fresh water tank until water comes out what i believe is the overflow. Problem is it siphons the tank dry. It doesn't happen every time so i'm having a difficult time figuring out how to stop it
My TT had an air vent over the fill inlet and would allow the pressure to equalize. This is draining from a tube next to my low point drains.
Any Ideas?
I'm not familiar with the FR's, (or most motorhomes for that matter) so I don't know how it's setup, but the fact that it's draining next to your low point drains, just to check, are you certain it's not the FW drain? Is that identifiable elsewhere?
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Old 04-27-2018, 02:56 PM   #10
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Hmmmm.
A question comes to mind.

An overflow tube/air intake probably should NOT reach down into the tank at all. The end of the overflow tube entering the tank should be essentially flush with the top of the tank.

This way, as soon as there is any air gap between the top of the water in the tank and the overflow tube, it breaks any suction or capability to siphon the contents out of the tank.

Is it possible that the overflow tube is entering the tank and reaching down to the bottom of the fresh tank? Is it attached to the correct location on the top of the tank?

If you think about a straw in a glass, it reaches down to the bottom of the glass, and it allows the straw to withdraw the entire liquid contents of the glass. But an overflow tube that doubles as an air intake to balance pressure when pumping has no reason to reach below the very top of the tank. If there is too much water in the tank, slightly pressurized water overfilling the tank will still escape out the overflow tube with essentially no difference in water pressure regardless of where the overflow enters the tank. The pressure needed to lift water from the tank level to the overflow port level will be the same.

But even if passing air creates a suction that starts a siphon, as soon as there is a bit of an air gap between the vent tube and the top of the water in the tank, the air gap should break the siphon action.

A fill pipe might be attached high on the side of the tank...for the sake of simplicity and easy installation This will enable easy gravity-feed filling (even if it has a connector for a pressurized hose). The overflow pipe might be attached very high on the side as well (instead of the top) to prevent kinks, etc. so you might lose a tiny bit of water from siphoning, but once there is a bit of air in the tank, the overflow pipe should suck air, not water.

Maybe your system is different in some way, but fundamentally the overflow pipe/air intake should not be buried deep in the water if for no other reason than incoming air must enter through water in the tank rather than simply add air into the top of the tank. Are the fill pipe and overflow pipe connections low on the tank or is the tank tilted to keep them buried in water?

Perhaps this response is off the mark, but in a properly designed and INSTALLED system, the overflow pipe should not be underwater enough to enable siphoning.
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Old 04-27-2018, 02:59 PM   #11
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my tank siphoned empty first time out. I added a screw on cap to the over flow drain line. once tank is full and water is coming out I turn of water and then screw on cap. Never forget to fill with cap on, don't know what would happen.
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Old 04-27-2018, 03:01 PM   #12
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I have a 2017 FR3. I once filled my fresh water tank and got out to the campsite and it was empty. I mulled over that for a long time and still do not know what happened and yes all drains were closed, head scratcher for sure and to top it off wife suggested I was maybe losing it?

The only theory I could come up with is this. I filled tank until water was pouring out of overflow (near low point drains) and immediately after shutting off tap and disconnecting hose I pulled unit ahead and it had a good lean on the side of overflow pipe. I didn't notice but I don't think water ever quit pouring out of overflow and maybe siphoned all the water out.

I still don't see how this could have happened but now after filling tank up to a few inches of top I double check there is no water leaving. Hasn't happened again.
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Old 04-27-2018, 03:03 PM   #13
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One other possibility.
If air can enter the fresh tank through another pathway, it's possible (unlikely) that suction at the end of the overflow pipe is strong enough to lift the water out of the tank once the siphon starts.
I can't really imagine how this could be, but if air is replacing the water during the siphon process, and if your tank is shallow enough, maybe....
That seems to defy physics, but stranger things have happened.

That raises the question, is there another air intake to the tank other than the fill pipe...which should be capped for travel.

Again, more speculation on my part. Siphoning typically requires an unbroken connection between the pick-up end of the hose/pipe and the water. Even the slightest air gap will break the siphon.
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Old 04-27-2018, 03:11 PM   #14
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Originally Posted by Leerich View Post

Thanks for all the responses I plan on putting in a valve. In regards to that is there any reason that compartment is walled of with a port in it? My hand barely fits through it and i can't see anything.
I think that is part of the winter package. Hot water heater and furnace is in same compartment so it would help keep pump etc. warmer. I took out partition (four screws) and glued some of that aluminum bubble wrap stuff to the inside for added protection in cold weather. If you unscrew cover on porthole you can easily see level of water with flashlight but I take the cover off unless needed. Would be impossible to winterize with it on. Hope that helps explain.
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Old 04-27-2018, 04:55 PM   #15
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I had the same problem with my 2011 Georgetown. My solution was to remove the overflow tube and drill a 1/8" hole in the "top" of the tube at its highest point. This point is protected by the clamp that holds it to the top of the compartment. The hole breaks the vacuum that the overflow siphon requires to empty the tank. The toughest part of this fix was removing the pipe clamp that seals the overflow tube to the tank's overflow port. When I reinstalled it, I rotated the clamp to make it much easier to tighten the clamp. I've fully filled the tank to overflowing a number of times since then and have never had the siphon problem.

It's also impossible for water to flow out of the hole I put in the overflow pipe. The pipe is larger than the inlet for the tank and the other end of the pipe, well below the bottom of the tank, has a self closing (rubber) valve that opens up to the full diameter of the overflow pipe.

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Old 04-28-2018, 11:45 AM   #16
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When I complained to the dealer about our water tank draining itself sometimes, they installed a longer drain hose with a few loops at the top, to help break the vacuum siphon effect.

Read these threads for more info...

http://www.forestriverforums.com/for...ng-106248.html

http://www.forestriverforums.com/for...ain-70142.html
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Old 04-28-2018, 08:08 PM   #17
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When I complained to the dealer about our water tank draining itself sometimes, they installed a longer drain hose with a few loops at the top, to help break the vacuum siphon effect.

Read these threads for more info...
........
Extra loops won't help once the siphon starts. The only cure is an air break to prevent the siphon from starting. You'd have to add a loop of hose that rose over 32' above the top of the tank to prevent the siphon. That's the maximum height that a siphon will lift water.
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Old 04-28-2018, 08:32 PM   #18
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Extra loops won't help once the siphon starts.
All I can say is that we had the problem occur several times during our first few trips, but it hasn't happened again in the 3 years since that mod.
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Old 04-28-2018, 08:39 PM   #19
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Extra loops won't help once the siphon starts. The only cure is an air break to prevent the siphon from starting. You'd have to add a loop of hose that rose over 32' above the top of the tank to prevent the siphon. That's the maximum height that a siphon will lift water.
Would that be 32 feet at sea level or would that change if you went to the top of a mountain?
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Old 04-28-2018, 08:44 PM   #20
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Being a non-believer in tank siphoning theory and I'll explain why. The overflow tube at the top of the tank is nothing more than a fitting attached to the top edge of the tank. There is no tube running into the tank as that would be stupid due to fluid dynamics and everytime you filled your tank and the water came out the overflow, it would siphon dry every time. There is more to this phenomenon than meets the eye.
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