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Old 06-16-2019, 09:46 AM   #1
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This fresh tank siphoning is killing me

Long story short. We filled up at home for a big trip to Moab. I notice water leaking out of the over flow drains the entire trip. Get to the site and gauge says 1/3 tank. No doubt we had less than half the tank because we ran it dry and had all sorts of room in the gray and black tanks.

Itís a Rocky Mountain Edition. Sure I live on the Front Range of the Rocky Mountains and I like the color scheme better than the regular style, but the main reason I went with it is because of the 80 gallon fresh tank. I email Jayco and they tell me itís something that happens. Take it back to the dealer so they can add more hose inside the tank to stop the siphoning. Ok, but Iím not giving it to those guys until the winter. Just home from work this morning and getting ready to head out to Black Canyon and Blue Mesa. Iím not in a rush so I figure let me screw around with this thing. It has two overflow tubes so I stick a valve on each. Then I dig out my old water meter I purchased years ago for my last trailer (never took it out of the package). I start filling and at 38 gallons it starts leaking out of both overflow valves. I keep going and at 58 gallons itís coming out the fill tube. I shut everything down and let it settle. I keep the overflow valves closed and slowly begin to fill. Immediately starts coming out the fill tube again. So it looks like I have a little less than 58 gallons in my 80 gallon tank.

Anything else I can do? Any suggestions? Thanks for letting me VENT!
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Old 06-16-2019, 10:48 AM   #2
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Put little 1/4 turn valves on the end of hoses. Turn them off "after" fill up and don't forget to open them when you get to campsite. Fix them later the way you want.
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Old 06-16-2019, 10:51 AM   #3
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Jayco's wonderful way of filling your tank. On my 2017 Greyhawk I would lose 1/3 of my 40 gals before I reached my boondocking site. Finally discovered the siphoning problem with these units.

This is a known problem with Jayco and has been discussed on this forum many times. I ended up putting valves on my 2 overflow hoses plus my vent hose. Many other people have done similar things with good success. I fill the tank and then close all 3 valves. When I arrive and am set up I will open only the vent valve. Works like a champ.

This method works as long as you remember to open the vent valve. I once forgot to open it and the tank built quite a vacuum and for some reason the level never came off full. When I finally opened the vent, you could hear the air being sucked in and the gauge then showed a lower value. Funny that the pump never slowed the water flow to the sinks.

As far as capacity, what is stated includes what is held in your water heater. I noticed this on the Jayco specs because my unit has a tankless water heater (groan) and my spec shows 6 gallons less than identical units with standard water heaters.

Wish I had a 80 gallon tank!
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Old 06-16-2019, 12:25 PM   #4
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https://www.jaycoowners.com/forums/m...cture6497.html
I added valves to the overflow hoses, also. Same as above, open them to fill the tanks, then close. Once on site, open them to use the pump. Don't be surprised to see some water come out once they're opened. I've noticed the tanks bulge slightly when full, and relieve themselves a little until they stabilize some.
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Old 06-16-2019, 05:53 PM   #5
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Ok, thanks. I totally agree with the valves and in fact that is what I did this morning. I secured a valve on each overflow tube. So with the six gallon water heater I have about 64 gallons out of 80. We just cruised in to Curecanti. I opened both new overflow valves and they are running hard. So the siphon is still holding true. Can I use the water pump with those valves closed? Or will it suck the plastic tank inside out? Ugh. What a pain.
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Old 06-16-2019, 07:04 PM   #6
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Don't these tanks have a air vent along side the water fill port?
When I am filling my tank, I can feel the air coming out this vent.
If the over flow valves are kept closed after filling, and the water pump is turned on, wouldn't the air vent prevent the pump from sucking (compressing) the tank
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Old 06-16-2019, 07:36 PM   #7
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Quote:
Originally Posted by RAurand View Post
Don't these tanks have a air vent along side the water fill port?
When I am filling my tank, I can feel the air coming out this vent.
If the over flow valves are kept closed after filling, and the water pump is turned on, wouldn't the air vent prevent the pump from sucking (compressing) the tank
What you are describing sounds like a gravity fill arrangement which does have a vent near the fill port (example picture below). Unfortunately those of us that have (had) the siphoning issue do not have a gravity fill port, we only can fill our tanks by using the City water connection and aligning our panel valves to send the water to the tank. Since our setups can cause full city water pressure to be directed to the tank Jayco installed several overflow lines on the tank to keep us from over-pressurizing and rupturing our tanks. Those same overflow lines serve as vent lines to admit air back into the tank when you are drawing water out of the tank since we don't have the high-mounted vent like a unit with a traditional gravity fill connection does.

There was a Seneca owner who purchased a used unit which, unbeknownst to the new owner, had shutoff valves installed in the overflow/vent lines. He unknowingly used the water pump for a while and collapsed his tank. I believe he was able to remove the tank and re-expand it back to shape and salvage his tank. Valves work, but one must be vigilant in their use.
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Old 06-16-2019, 07:39 PM   #8
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We have the twin FW tanks, and only the front one is vented to the water fill fitting, like the one pictured above. The rear one is connected to the front by way of an equalizing hose. So yes, you need to open the valves to use the pump. You probably can get away with leaving them closed for a short while, using the pump until the overflows slow down. The pump will cause suction on the rear tank if the overflow valves are left closed.
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Old 06-16-2019, 08:48 PM   #9
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Quote:
Since our setups can cause full city water pressure to be directed to the tank Jayco installed several overflow lines on the tank to keep us from over-pressurizing and rupturing our tanks. Those same overflow lines serve as vent lines to admit air back into the tank when you are drawing water out of the tank since we don't have the high-mounted vent like a unit with a traditional gravity fill connection does.
OK, I understand the need for the multiple overflow/vent tubes (my unit has 3) so you don't over pressure the tank when using city fill.

What I don't get is why they continue to siphon. If they are vent or overflow tubes, aren't they mounted in the TOP of the tank. I can see some sloshing when moving, but how does the water continue to siphon when stopped, if these are in the top of the tank? Once the level drops an inch, it should stop. Right?

Do they have hoses internally in the tank that run down on the inside? This would be the only way it would continue to siphon, but if the ends of those hoses are in the water, they wouldn't vent???

Like the top ports in this tank:

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Old 06-16-2019, 08:56 PM   #10
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Excellent question! I've wondered the same, but can't see/tell how far into the tank they are. Maybe someday I'll drop the rear tank, just to take a look. You're right, they should be just at the top, and siphoning should stop once the water's not touching the hose. Goes back to siphoning gas out of cars. It only took a second for the flow to stop once out of the gas.
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