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Old 08-25-2016, 02:42 PM   #1
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Fix for Fresh Water Tank Siphoning Spilling Overflowing Problem

Like many of you out there, I was afflicted by the siphoning effect on my fresh water tank. I have a 100 gallon tank on my coach and would lose up to 1/3 of my tank in transport to my camping location. For those of you that like to dry camp like I do, it was devastating.

My Rig: 2015 Newmar Ventana Diesel

Fresh water tank location: Cargo door behind pegboard shown in pictures

My Fix: The short answer is that I placed an inline ball valve on the overflow line. I will detail the steps below:
1) Removed peg board and cut out the square 10" x 10" access door
2) Installed the black hinges and sliding lever lock and reinforced the pegboard in the back with 2" aluminum bars
3) Cut the overflow line which is 1 1/4" ID and reduced it down to 3/4" and installed 3/4" ball valve
4) Used two screw straps to secure the newly installed valve to the wall
5) Have a beer and enjoy the extra water on your next trip!

Now all you have to do is keep that valve "Open" unless you are driving to your location and zero water will spill. Already tested the setup on a 5 hour drive and didn't have any spillage.

The added benefit of this fix is that I can visually see exactly where my water level is by opening that access door. On my particular coach, it wasn't a very easy fix as you need quite a few tools to do the install, but if you have the tools and a few hours, you can do a similar setup on your rig.
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Old 08-25-2016, 02:43 PM   #2
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Here is one more picture.
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Old 08-25-2016, 03:30 PM   #3
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If that is the tank vent, you will blow the tank if you ever forget to open it while filling. Using water from the tank will collapse it if the vent is closed. Also, if the check valve in the water pump ever leaks you will get the same result.

Too many of these faulty designs have been produced. The correct and safe fix is to vent the tank well above the water level. The word siphon is not correct, it is simply a spill, siphoning requires that the exit pipe be below water level. The manufacturers just want to save a few bucks and ignore the fact that water runs downhill.
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Old 08-25-2016, 03:41 PM   #4
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Quote:
Originally Posted by lynnmor View Post
If that is the tank vent, you will blow the tank if you ever forget to open it while filling. Using water from the tank will collapse it if the vent is closed. Also, if the check valve in the water pump ever leaks you will get the same result.

Too many of these faulty designs have been produced. The correct and safe fix is to vent the tank well above the water level. The word siphon is not correct, it is simply a spill, siphoning requires that the exit pipe be below water level. The manufacturers just want to save a few bucks and ignore the fact that water runs downhill.
The tank itself will never blow, that cheap 1 1/4" flex hose is the weakest link for sure. I was not able to get "my" flex hose any higher in my coach configuration, as there is a black water tank / walls above where that hose is. You definitely need to be actively opening and closing that ball valve when appropriate, which is a pain, but better than losing a third of my fresh water in transit. Obviously this isn't the fix that NASA would use on the space shuttle, but it works for me and for anyone else having this problem. I agree that if you can just run that flex hose a foot higher than the top of the tank, that is the safest and best way to go, but not an option that I had.
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Old 08-25-2016, 04:09 PM   #5
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Quote:
Originally Posted by lynnmor View Post
Too many of these faulty designs have been produced. The correct and safe fix is to vent the tank well above the water level. The word siphon is not correct, it is simply a spill, siphoning requires that the exit pipe be below water level. The manufacturers just want to save a few bucks and ignore the fact that water runs downhill.
Siphon may not be the perfect description of this situation but we all know exactly what is meant. And running a vent well above the tank is most likely not an easy thing to do but the valve certainly is a good fix.

Quote:
Originally Posted by Bobby.D View Post
The tank itself will never blow, that cheap 1 1/4" flex hose is the weakest link for sure. I was not able to get "my" flex hose any higher in my coach configuration, as there is a black water tank / walls above where that hose is. You definitely need to be actively opening and closing that ball valve when appropriate, which is a pain, but better than losing a third of my fresh water in transit. Obviously this isn't the fix that NASA would use on the space shuttle, but it works for me and for anyone else having this problem. I agree that if you can just run that flex hose a foot higher than the top of the tank, that is the safest and best way to go, but not an option that I had.
Bobby, I did this exact same fix for mine and it has performed perfectly since I did it. Like you, I would much rather turn a valve on or off than to have 30% of my water trailing behind me on the ground.
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Old 08-26-2016, 06:45 AM   #6
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Quote:
Originally Posted by Bobby.D View Post
The tank itself will never blow, that cheap 1 1/4" flex hose is the weakest link for sure. I was not able to get "my" flex hose any higher in my coach configuration, as there is a black water tank / walls above where that hose is. You definitely need to be actively opening and closing that ball valve when appropriate, which is a pain, but better than losing a third of my fresh water in transit. Obviously this isn't the fix that NASA would use on the space shuttle, but it works for me and for anyone else having this problem. I agree that if you can just run that flex hose a foot higher than the top of the tank, that is the safest and best way to go, but not an option that I had.

Is there a reason that you couldn't have come thru the pegboard and then up as high as possible, and then return back down thru the pegboard? Using rigid pipe to do that would have a better appearance and be less prone to damage. Just a thought.

I had a similar situation, but there was no where to go but out thru the wall, so that is how I fixed the problem. There is no way that I was about to seal off a tank and have the potential for major damage.
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Old 08-26-2016, 08:16 AM   #7
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Originally Posted by lynnmor View Post
There is no way that I was about to seal off a tank and have the potential for major damage.
The water tank is not really getting sealed off, at least on mine. You still have the gravity fill door which lets air into the tank and will let pressure vent, after all the line going into the tank is not filled or under pressure. The only thing the valve does is stop the water from draining needlessly from the over flow tube which is there to aid venting when filling the water tank.
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Old 08-26-2016, 09:03 AM   #8
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Quote:
Originally Posted by lynnmor View Post
Is there a reason that you couldn't have come thru the pegboard and then up as high as possible, and then return back down thru the pegboard? Using rigid pipe to do that would have a better appearance and be less prone to damage. Just a thought.

I had a similar situation, but there was no where to go but out thru the wall, so that is how I fixed the problem. There is no way that I was about to seal off a tank and have the potential for major damage.
That is definitely another good option.
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Old 08-26-2016, 07:08 PM   #9
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Bobby, fleetwood did the exact same thing as you did to my coach. From the factory, fleetwood put a ball type check valve in the vent line, if pressure overpowered the spring tension in the valve, it would come out the overflow. Problem was that the vent line was installed on the side of the tank a couple inches down from the top. The spring valve was very weak and I would lose roughly 20 to 30 gallons of water while driving. We boondock at racetracks all the time and that extra water was very important to us. I took it to the fleetwood factory and they plumbed in the same ball valve you had but its all done in pvc. I keep it open while filling the tank and when it starts coming out the overflow, I close the valve and continue filling until it spits out the small overflow vent next to the gravity fill. I now have right around 105 gallons on board and life is good. If I were to forget and overfill the tank, it will squirt out the small overflow vent so its not really a big deal. I will have to explain it to the next owner should I happen to sell the coach. The upside far outweighs the down side.
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Old 08-26-2016, 07:26 PM   #10
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Prior motorhome, two fresh water tanks, the vent hoses looped above the tanks by an inch or so, it was enough to defeat the "siphon" effect. Open vents were necessary to balance the water level in the 2 tanks. Before the dealer put the large loops in the vent lines I would lose a lot of the water enroute. Vent lines were clear 3/4 inch tubing.
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