Fresh Water Tank Overflow

[Riich]

I know this topic has been about beat to death, and everyone has their fixes to prevent losing all their water. But I wonder about another possibility.



This is my filler hole. I have had other RVs that never had the overflow hoses and I just filled until water spewed out the fill hole. I'd then screw on the cap and head out and never had an issue. Isn't the screen you see in the photo a vent for the fresh water tank? Why is that not sufficient for venting the tank? Especially when it was on my other RV's, or it had to have been since it is all they had. It's not like we use a fast supply of water that requires any heavy venting.

I'd like opinions, surely someone else has thought about this and tried it. If not I'll be the guinea pig and give it a whirl. I'm tired of plugging and unplugging the so-called overflow hoses. It just shouldn't be necessary.

I know, some of you think the design engineers are all it and everything is perfectly engineered, but sometimes I wonder.

I'd like opinions.

Thanks.

[Jolvi]

Exactly what I wondered, I mean the overflow comes out of the tank makes loop and goes back down to the floor but you can see that vent you are talking about.

[JimD]

My old camper had an external fill a bit like yours. It had a small vent hole next to the large filler hole. Never had a problem.

Newer fill systems use a direct pressurized hose to the tank. My tank has 3 overfill hoses (maybe 2 overfill and 1 vent) that will suck the water from the tank. Learned that the hard way.

My second and last fix was to extend the 3 hoses up into my outside shower/fill bay. I put valves on them but don't need to close them to prevent siphoning out. Getting the hoses above tank level was my solution. I am actually able to completely fill the tank, more than before. No problems whatsoever.

[Bob K]

Yes, that screen covers the vent hole. On mine, it leads to a clear hose that connects to a fitting on top of the tank.

[Robbbyr]

When you have the external fill and vent like pictured you won't lose water while driving. But most Jayco motorhomes, and many of their towables, do not have that gravity fill. You fill the tank in those rigs via a valve arrangement that directs water from the City inlet to the tank. Because they are plumbed that way, those rigs have multiple overflows to prevent the tank from splitting apart when full when full city water pressure is coming into a full tank. Those same overflow lines allow air back into the tank as water is drawn out by the water pump. Without the vents the tank will eventually collapse. The vent on a gravity fill is the screened vent/overflow visible above.

When a motorhome or towable has the fill from the city inlet there is a tendency for the water to siphon out of the water tank while driving. Some lose half of their tank while driving. I was one who it used to happen to. But I designed and installed an air gap manifold that "breaks" the siphon effect. But it still allows the original overflow capacity if needed, and it still allows air to reenter the tank as the water pump empties the tank.

[norty1]

Interesting, I have never heard about this. I don't understand the hot water line's part in this solution.

[Robbbyr]

Originally Posted by norty1

Interesting, I have never heard about this. I don't understand the hot water line's part in this solution.

I actually has nothing to do with the siphoning problem. I installed a hot water recirculation system on my Seneca to prevent wasting water down the drain waiting for it to get hot. So I have a solenoid valve controlled by a switch with a 30-second timer that takes water from my furthest hot water fixture (shower) and directs it back to the fresh water tank via my manifold. Hit a switch, solenoid opens for 30 seconds, hot water flows back to tank, instant hot water at all fixtures!

Red pipe in installed manifold picture in prior post is the hot line coming back to dump into tank.

[Riich]

Originally Posted by Robbbyr

When you have the external fill and vent like pictured you won't lose water while driving.

Understand, I have the external fill and vent I posted a photo of. I ALSO have two overflow lines under my trailer that start spewing out water when the fresh water tank is almost full. I have learned to plug them with rubber stopples (like rubber corks) before leaving home or a 1/3 of my water will syphon out. I don't care to remove the BS covering under my camper to rework the overfill hoses unless I have to. I'd like to cap them for the summer and just use the vent in the photo. If that would work?

I realize some people have access to their overfill hoses, I don't. I wish I did. Mine stick down less than an inch below the undercarriage covering.

[Robbbyr]

Originally Posted by Riich

Understand, I have the external fill and vent I posted a photo of. I ALSO have two overflow lines under my trailer that start spewing out water when the fresh water tank is almost full. I have learned to plug them with rubber stopples (like rubber corks) before leaving home or a 1/3 of my water will syphon out. I don't care to remove the BS covering under my camper to rework the overfill hoses unless I have to. I'd like to cap them for the summer and just use the vent in the photo. If that would work?

I realize some people have access to their overfill hoses, I don't. I wish I did. Mine stick down less than an inch below the undercarriage covering.

On my two prior Class C units I only had the gravity fill/vent arrangement. On both units I could see the tanks inside cabinets and the only connections to the tanks were the larger fill line from outside, the vent that also connected back to the fill, and the outlet to the pump. I never lost water and never had any issues. So why Jayco felt you needed extra vent/overflow lines escapes me, unless there is a way to send water from the city inlet and they felt it necessary to add them to prevent over-pressurizing the tank.