This fresh tank siphoning is killing me

[tom463219]

Breaking the syphon on a fresh water tank. Sent to me 2 years ago from JAYCO. Why the heck don't they do it at the factory?

[RetiredOne]

Getting one vent higher will break a siphon.... but I still don't understand and no one has explained......

Those 3 fittings are screwed into the Top of the tank. Once the water level gets below the bottom of the fitting, the siphon has to stop, as it's no longer physically touching the water level. Yeah, you could get some sloshing out stopping and starting, but when water seeks it's own level, the siphon will stop.

The only way the siphon can continue is if there are sections of hose, attached to those fittings, that are submerged into the tank. There's zero reason for that, if they are overflow or vent hoses, unless Jayco really screwed up the installation.

Has anyone actually confirmed if a hose runs from those 3 fittings down into the tank?

[tom463219]

When making right turns (such as getting on the interstate off a cloverleaf ramp), I could look out the side mirror and see lots of water gushing out the vents. It appeared to stop when straightening out. It would do this constantly on right turns. I would lose a lot of water. Don't really think it was syphoning. Just flowing out the vents when water was moving in the tank from turning. I installed 3 shut off valves and that stopped the water loss. I have shut 2 off and left only 1 open. Water loss was very minimal that way, and tank was still venting. I open all 3 when filling the tank, or when arriving at campsite.

[RetiredOne]

I can see some of the sloshing you describe on right hand turns, but other people report that when they stop they still see water siphoning, so that's strange.

Others have reported that they left with a full tank of water, and when arriving at their destination, they're down to 1/3 of a tank. Do you think that much can drain out by turns and sloshing?

[tom463219]

I have lost 2/3 of my water in the past. Sounds crazy that so much water would escape. Since putting on the valves, I don't lose it anymore. I said that when making right turns I could see the water coming out, but it was probably escaping when braking and accelerating too, I just couldn't see it.

[Bullitt6283]

Seems to me that the water is lost through the vents not by siphoning, but due to the sloshing of water when driving, driving and stopping on hills, etc.
This effect is greatly aggravated by the tanks being proportionally long and shallow.
I lost a lot of water until I installed valves on the vent lines. The 2016 29MV has a smaller tank than later models, and I really hate the lessened capacity.

[jd99336]

Originally Posted by Bullitt6283

Seems to me that the water is lost through the vents not by siphoning, but due to the sloshing of water when driving, driving and stopping on hills, etc.
This effect is greatly aggravated by the tanks being proportionally long and shallow.
I lost a lot of water until I installed valves on the vent lines. The 2016 29MV has a smaller tank than later models, and I really hate the lessened capacity.

Since there appears to be multiple threads on this topic on which I have opined, I will say that the last few posters here are correct. This cannot be a "siphon" as air in the tank would benefit the siphon not stop it. Each line can form it's own siphon if submerged in water (so why doesn't it stop when level drops below the vent tank entry) and has water in the tube below the level of the water in the tank. Siphons are about gravity of the lower tube/water creating suction. Once air enters at the top, suction is broken and siphon should cease. Rather, I believe the issue is turns and braking causes the vents to become "drains". While siphoning may assist in the process it cannot be the actual cause. Either the vents have to be well submerged in the tank or the water is just sloshing out through the vents.

As an experiment I parked flat and level. I filled my tank to the point water was coming out of the vents then shut it off. The water ran for a minute or so more (partly siphon, partly as the flexible tanks likely swell to a slight over capacity) then it stops. Tanks register full. If a true siphon, the water would have kept coming.

The true solution is getting the vent lines above the tank level, or plugging the vents. Others have done the air gap valve trick and report success. I can't explain that, other than perhaps it is that the air gap valve is above the water level.

[SkyBound]

When I am filling, I wait until the water starts flowing out of my 2 overflow tubes (two 42gal fresh tanks linked together for 84gal+6gal water heater) and then I link the two tubes together using a 6 inch piece of hose. I then can put another few gallons into the tanks beyond that (guessing 10?) and then head to my campsite with the tanks linked and not lose any water. Without this trick I am certain I would only be using a fraction of my total capacity.

[Quantum]

I raised my vent line above my tank. I connected it to the air inlet port on my gravity fill.

[Learner]

As the owner of a new 2019 Jay Flight 224 bh, this has been a very useful thread.

My RV has a gravity fill 42 gallon tank with two overflow tubes and one vent tube. The first time I tried filling it to the top I saw water coming out of the overflow tubes before the tank was actually filled, and before it ever came out of the vent port near the fill port.

I kept filling anyway until the water was starting to slightly back up out of the fill port. However, the vent port alongside the fill port did not seem to have water coming out of it. So I do not know if the tank ever was truly completely full, except that the level sensor did read full.

Since I actually do have a vent line (or at least a port where there's a vent screen near the fill port) I will probably try adding shut-off valves to the overflow tubes, per the advice of some here.

It also occurs to me that part of the issue with mine may be the insulation on my unit, since I have the full underbelly wrap.

There appears to be so much insulation stuffed on top of the underbelly foam panels that it causes the panels to bow down significantly. My guess is that this puts pressure on the fresh water tank, pushing up on the bottom of the tank somewhat, and thereby causing water to try to flow out of the overflow tubes before the tank is actually full.

This is however just a guess, since I cannot actually see the tanks due to the underbelly wrap.

Best wishes,

[G.Smith]

Have you considered a Vacuum Breaker in the high point of your overflow line? Allowing air to enter the line will break the siphoning effect.

[Bullitt6283]

Originally Posted by Learner

......There appears to be so much insulation stuffed on top of the underbelly foam panels that it causes the panels to bow down significantly. My guess is that this puts pressure on the fresh water tank, pushing up on the bottom of the tank somewhat, and thereby causing water to try to flow out of the overflow tubes before the tank is actually full......

Assuming your 42 gallon tank, with water weighing 8 pounds per gallon, it may be unlikely that the insulation is deforming the bottom of the tank upwards.


About your other comment about filling.... These tanks can be long and wide but not very tall. This means that if the tank is leaning towards the side where the overflows are, there may be significant volume of the tank which would not get filled.


.

[33 RLDS]

Originally Posted by Robbbyr

Unfortunately those of us that have (had) the siphoning issue do not have a gravity fill port,

I have a gravity fill port and did suffer the dreaded siphoning problem as well

[oldmanAZ]

Originally Posted by G.Smith

Have you considered a Vacuum Breaker in the high point of your overflow line? Allowing air to enter the line will break the siphoning effect.

Welcome to the forum.

An excellent idea, but many (most?) of us do not have access to the top of the fresh water tank(s). If we did, we'd try either extending the overflow line to be higher or install a vacuum breaker.

[windywy]

The question is why after years of making these campers by the thousands Jayco has never addressed this issue?

[TonyCO]

Thanks for the comments! Back from my trip so I have a few more thoughts from the beginning. I put the valves on both overflow tubes. Was only able to get about 64 gallons into the 80 gallon tank before the water just kept running right back at me from the fill tube. Shut the valves off and drive about 200 miles over Kenosha and Monarch Passes. As soon as I get to the site I open the valves and water immediately starts to flow. I turn on the water pump and let water flow through the kitchen sink hoping this would somehow stop the overflows from draining. I let the kitchen run for about two minutes with no change so I just shut it off. At some point during the night the water did stop flowing from the overflow tubes. We used a little bit of water for those two nights and then headed to another dry site. I dumped at Elk Creek and decided I would fill up for the heck of it. I took on another 24 gallons and nothing was coming out the overflow tubes so I left them open for the drive. I stop about 40 miles later and water was pouring out both overflows. I turned the valves off for the rest of the drive then opened them at the campsite. Once again water is pouring out both overflows so I just shut them down and used the water pump a few times after dinner. I left them closed until this morning and as soon as I woke up I opened them and nothing was flowing. Drove all the way home with them open and not a drop out of them. Definitely have at least 40 gallons in the tank. Who knows????

[Bullitt6283]

It is evident that Jayco's vision of how their products are (or should be) used is different from reality.

Vision: When boondocking, fill your water tank when arriving at a camping grounds.
Reality: Water is not available at the site, and the tank must be filled before travel.

Solving most of this problem would be so inexpensive to execute during manufacturing that one wonders if they care at all. Something as simple as extending the tank vent line(s) a foot higher in elevation above the top of the tank could eliminate water loss due to sloshing during travel.
.

[Rustynuts]

I agree, easy fix but they don’t care. This water loss problem is not just Jayco, lots of other manufacturers have the same issue.

[TonyCO]

I just fired off an email to Jayco. Made me feel better anyway. My 2015 Keystone Laredo never had this problem. I understand none of these things come off the line perfectly, but I really think this is ridiculous. Especially when the rep knows exactly what the problem is and tells me to take it to the dealer. Literally another minute on the line and I would never know this problem existed.

[RetiredOne]

Originally Posted by Rustynuts

I agree, easy fix but they don’t care. This water loss problem is not just Jayco, lots of other manufacturers have the same issue.

Probably because they buy the water tanks from the same source and route the vents the same (and easy) way.