225MLSW fresh water overflows while towing

[PopBeavers-KEY]

My 2025 Jayco Jayy Flight 225MLSW is now one year old. I had it to the dealer recently for various warantee issues one of which was the fresh water tank loses water while towing. The water is not leaking into the insulated belly. The dealer said it was probably siphoning out the over flow tube. They added a loop to the over flow line. Today at home I tested it. I filled it until it started to overflow. This is I think 74 gallons. I towed it 45 miles in the mountains of the Sierras. When I got home the guage showed 2/3 full. I added 31 gallons to top it off back to where it was starting to overflow. That is nearly half of the 74 gallons that is leaking out.

Has anyone else experienced this?

What did you do to fix it?

I am considering putting a valve on both over flow hoses.

 

[Grumpy]

Very common issue, we had the problem with our 08 SENECA. Valves worked for me, but you have to remember to open when filling and again when using the pump. Some JOF members made manifolds to stop the siphoning.

 

[JFlightRisk]

We have twin tanks, and I added valves to the overflows. The main cause is that the tanks are very shallow to fit between the frame rails. If your frame is 6" high, so is your tank.

There's a huge surface area of water to slosh towards the overflow fittings at the upper edge of the tank. There is nothing sticking inside the tank to actually siphon it completely empty, just the air moving past the hose to draw out what's being sloshed into it.

Like Grumpy mentioned, I do have to remember to open the valves to fill them, close to travel, and re-open them to use the pump. We don't travel with them full but can lose some from the fill station to the campsite. Especially if the site slopes to the driver's side before I can get it level.

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[Kevin Cooper]

The water flows out the tubes when making hard turns on our Alante. So, I slow down on corners if I have a full tank. Generally I only have 1/3 tank so, no issues.