Fresh water tank siphoning defect

[Geo9350]

Hi I have the fresh water tank siphoning defect. I read where people took it to the dealer to have it fixed but my nearest dealer in too far away. What did they do to fix it? Mine siphons off to where I only have 1/3 of a tank of water. Must be an easy fix.

[Shane Wood]

You can install a pex shutoff valve on the overflow line. Fill the tank and when the water starts to flow out the line turn the valve off

[Ford truck guy]

Originally Posted by Shane Wood

You can install a pex shutoff valve on the overflow line. Fill the tank and when the water starts to flow out the line turn the valve off

X2 ... under $8.00 at the big box stores . . BUT remember to leave it open once you get to were you are going.... And more importantly , make sure it is open when filling the tank...

[atom ant]

I valved mine



The actual overflow is between the drains

[830hvacman]

Originally Posted by atom ant

I valved mine



The actual overflow is between the drains

In your last picture - looks just like mine - mine is the fresh water vent. Normally it is connected to the water fill valve assembly, between the city water and water tank fill. there is the small 3rd fitting w/ screen wire. All my previous units had the tank vent connected near that fill valve assembly, but not this one.. Well I guess both the vent and overflow don't have screens now..

[RCAircraft]

On our 36RL there are two overflow drains. Both can drain off a third or more of the fresh water. Until I can remember to pick up some valves I inserted a "plug" in both lines. The plugs are caps from a plug-in room freshener. They are tapered and fit like a glove.

[atom ant]

Originally Posted by 830hvacman

In your last picture - looks just like mine - mine is the fresh water vent. Normally it is connected to the water fill valve assembly, between the city water and water tank fill. there is the small 3rd fitting w/ screen wire. All my previous units had the tank vent connected near that fill valve assembly, but not this one.. Well I guess both the vent and overflow don't have screens now..

Ya, I think it is because the fill is inside of a cupboard. If it splashed out on travel it would soak your cabinet. All mine that were connected to the fill on prior units were also on the outside wall.

[Geo9350]

Thanks all, I went out today and pulled the wall down so I could get to the hoses hooking up to the top of the tank. I thought maybe they had the overflow hose pushed down into the tank because it was siphoning off to 1/3 of a tank. So I unscrewed the hose off the top of the tank and found that that was the top of the hose, there was no hose going down into the tank. It didn't make sense to me why it would siphon with it ending at the top of the tank, you would think once the water level dropped down to below the top of the tank it would stop running out, but nooooo. Anyway I took your advise, went down and bought a pex valve and put it on the end of the hose sticking out the bottom of the RV. Doesn't make sense, but for some reason this tank must have something down into the tank from that connection so it is below the top of the tank and once it starts running it will siphon off 2/3s of the tank. I wonder if the dealers had to replace the tank to stop this problem. Our RV was made in 2013 I guess they had that problem in that yr and fixed it in the later models.

[Ford truck guy]

Originally Posted by Geo9350

Thanks all, I went out today and pulled the wall down so I could get to the hoses hooking up to the top of the tank. I thought maybe they had the overflow hose pushed down into the tank because it was siphoning off to 1/3 of a tank. So I unscrewed the hose off the top of the tank and found that that was the top of the hose, there was no hose going down into the tank. It didn't make sense to me why it would siphon with it ending at the top of the tank, you would think once the water level dropped down to below the top of the tank it would stop running out, but nooooo. Anyway I took your advise, went down and bought a pex valve and put it on the end of the hose sticking out the bottom of the RV. Doesn't make sense, but for some reason this tank must have something down into the tank from that connection so it is below the top of the tank and once it starts running it will siphon off 2/3s of the tank. I wonder if the dealers had to replace the tank to stop this problem. Our RV was made in 2013 I guess they had that problem in that yr and fixed it in the later models.

I have a 2016 that had the same issue... I put a valve on it before it could happen while camping.. no more issues

[RW Cal]

Here is my theory....
i believe there may be a float valve inside the fresh water tank that is connected to the overflow line, the valve is like the one in a standard toilet, but the overflow is actuated when the tank is full. I think the valve stays on as the tank drains down to about 1/3 and then shuts off. If you watch your home toilet tank flush it seems to make sense. It may be that the wrong kind of float was installed or that the float needs adjustment, but I doubt if that is easy.
I like the manual cutoff idea and plan to do that and not worry about it!

[RW Cal]

I searched the internet and all kinds of rigs have this same problem. They even say they go from a full tank that starts to overflow down to 1/3 of a tank when it stops!

[RW Cal]

OK, I guess I will debunk my own theory. It is a syphoning issue. Some RV manufacturers are even installing the shutoff valve in the overflow line!