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Old 01-14-2020, 11:39 AM   #1
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Gone through 2.5 tanks of water in 3 days

I just picked up my greyhawk 30z 3 days ago with a tank of freshwater. By the next morning I had only a third of a tank filled with freshwater. I took it back to the dealership to have the tanks filled again. The following morning the tanks showed that it was empty. The tanks were nearly empty indicating that the sensors were working correctly. The problem appears to be dad when driving the vehicle on an incline the water rushes towards the overflow hoses and empties the tank. Has anyone had this problem and what was the solution to it?

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Old 01-14-2020, 12:03 PM   #2
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There have been discussions here from some who have had the same issue. I have not experienced it. I assume it does not show any sign of draining while not in motion? I've heard some owners have installed a shutoff valve on the drain and/or vent, but I would be careful to research it before doing so.

You should be able to find this topic by searching through the tech topics at the lower sections of the Forum page.

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Old 01-14-2020, 12:09 PM   #3
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Old 01-14-2020, 12:10 PM   #4
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Yep, Jayco builds in auto-siphoning into their fresh water tanks Do a search on the forums, there are numerous threads about it and really its not just a Jayco problem. I had the same problem on our Seneca, and you basically have to create a vacuum break to stop the siphon, some put a shut off valve on the tank vents but I dont like that option as you have to go out and open it before use and if you forget, you can collapse your tank with use or balloon it while filling causing structural damage.

Here are a few links

On our Seneca I was able to re-route the vent lines across the top of the tank and into a PVC chamber higher then the tank and then to the drains. This has stopped the problem completely.
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Old 01-14-2020, 12:31 PM   #5
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You may get a lot of replies as this subject has been discussed many times. It is a very common issue because of the way Jayco fills their tanks.

My 2017 Greyhawk would lose 1/3 of a tank between home and our site. Water flows out the overflow hoses. This really came to a head when I pulled in at my propane fill station which was angled downward. While I sat there water was flowing out of my rig all over the place.

I put shut off valves on all 3 hoses and that totally solved my problem. Many others have done the same thing. You just have to remember to open the valves when filling or you will blow up your tank. Also need to open one hose while camping to allow air to enter.

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Old 01-14-2020, 01:43 PM   #6
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Lots of discussions regarding FW tank siphoning.

What a number of people have done is add a shutoff valve on the overflow pipe. You MUST open the valve when you fill the tank, or you risk rupturing the tank.

I found the vent/overflow tube, and pushed it up as I as I could and still have it sticking through the floor. I went inside of my TT, and I clamped the hose to the wall, with the loop as high as I could. Before I clamped it to the wall, I found after a number of trips the hose would vibrate back down and the tank would siphon again. Since adding the clamp, I have never had any siphoning.
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Old 01-14-2020, 01:58 PM   #7
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My tank has 3 vent hoses. I put 1/4 turn valves on 2 of them and left the third alone. This allows for passage of air and overflow when filling as well as passage of air while using water, and doesn't drain the tank in transit.

If I'm filling the tank, sometimes I will remember to open the valves, but my tank fills very slowly, so not opening the other two valves has never caused a problem.

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Old 01-14-2020, 02:31 PM   #8
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I bought one of these https://www.amazon.com/Rainwave-RW-9...CYEQKZA29QEFEK to measure the amount of water going onto my tanks. I have twin 40 gallon tanks and when the meter reads 76 gallons I slow the fill rate way down and this seems to help with the siphoning effect. When it starts to dribble out the overflows, I plug them up and drive to my campsite, unplug and tanks full.
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Old 01-22-2020, 11:01 AM   #9
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Thanks for everyone's help

I gave a lot of thought to everyone's input. Due to the shallow nature of the tank and the position of the overflow hoses, I think there are two issues - syphoning and general water loss due to the angle of the vehicle. I routed the lines into a neighboring storage compartment, connected valves to the lines, and adde hose to exit the compartment. This seems to be working. I put a towel over the steering wheel of rig as a reminder that I need to shut off the valves before I travel. I put up a sign near the switches that need to be changed before filling the tanks to remind me to open the valves as well. Thank you for everyone's help I appreciate it.

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water tank full?, water tank leaks

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