Fresh Water Tank Vent syphoning mitigation

[Paul Adams]

We just sold our Reflection 337RLS, which we had for 7 years and bought a new Reflection 226RK. We had no problem with water loss with the old trailer, but I have yet to arrive at our destination with the fresh water tank reading anything by empty, regardless of the level when we set out. I have read a number of threads on this problem and the solution is to add a valve at the overflow outlet. I have two questions that perhaps someone can help me with. First there are two lines under my trailer, see the enclosed picture. One is the overflow, but what is the other? I don't know which one the water is coming from as it only drains when we are moving, so which one do I put the valve on?

Does anyone have an arrangement sketch for the fresh tank piping that shows any loops in the overflow drain and/or vent piping?

[WhittleBurner]

We just sold our Reflection 337RLS, which we had for 7 years and bought a new Reflection 226RK. We had no problem with water loss with the old trailer, but I have yet to arrive at our destination with the fresh water tank reading anything by empty, regardless of the level when we set out. I have read a number of threads on this problem and the solution is to add a valve at the overflow outlet. I have two questions that perhaps someone can help me with. First there are two lines under my trailer, see the enclosed picture. One is the overflow, but what is the other? I don't know which one the water is coming from as it only drains when we are moving, so which one do I put the valve on?

Does anyone have an arrangement sketch for the fresh tank piping that shows any loops in the overflow drain and/or vent piping?

Those look like the low point drains except I don't see the caps on he ends of them. The overflow hose should be behind the drivers side rear tire. Next to the white handle for draining the fresh water tank.

[north channel novels]

Hmm. Our 230RL has one vent. Same blue 3/4 inch blue plastic as those in your picture. Is one of those by any chance the drain hose? (Ours drains through an adjacent white gate valve.)
Quickest way to figure out which one is the vent, fill your tank to overflowing and see which one the water is running from.

[KDutchover]

We have a 2018 Reflection 230 RL which we bought new, and are really enjoying. BUT at the beginning, when we filled our fresh water tank before heading on the road, we often ended up with little more than 2/3 of a tank when we arrived at our destination. No leaks ... nothing left turned on ... waste tanks hadn't gained what the fresh water tank had lost. Strange.
One day I looked back as I was pulling out on the road with a full tank, and could see water splashing out on the road behind me. I began to realize where our water was going. With the wide, shallow tank full, once the water started to run out the vent, it continued to be sucked out by syphon action until a bump in the road, or change in direction caused the syphon action to be interrupted.
We don't normally travel with a full tank unless we are headed for unserviced campgrounds or places with uncertain water quality. So when we do fill before starting out, it is a little disconcerting to arrive with less than our anticipated water ration.
Once I figured out the problem, the fix was simple. I cut several inches off the vent pipe and cemented on a 3/4" (id) plastic (or ABS) water tap from the hardware store. It gets turned off before we roll (a new item on our pre-departure check-list) and opened as soon as we arrive, or stop to add water to the tank along the way.
Attachment 29769

Our 2022 280RS also has two overflows for the fresh water tank. Our 2019 230RL only had one. A call to Grand Design revealed that the overflow T's at the tank. This new arraignment helps stop siphoning. We still lost water upon hard right turns with a full tank but would stop after the turn. Two sharkbites valves solved the problem.