Fresh water holding tank overflow HELP please

[Iowa_Cowgirl]

I am new to RVing, am getting ready to go camping tomorrow morning. I filled the fresh water holding tank this evening. I ran the hose pretty fast and my tank overflowed. How can that be? I thought the water system was a closed system other than putting water in the tank and getting it out via shower or faucet. I was told by the guy who built my rv that if I put the water in too fast, the tank can run over. Is that true or is he just pulling my leg?
I should be specific that my rv is a gooseneck horse trailer and the dressing room had a custom living quarters installed just recently. This is my first trip with the conversion installed.
Please advise. Thank you.

[westend]

If your rig has a tank with a tube attached to the vent and if that tube is inside the dinette area, when you fill the tank fast, the vent tube may be carrying water to the inside of the camper.

At the point you're at, it is best to access the tank and check all fittings for any leaks.

[mlts22]

The FW tank should splash out the overfill port, or if the pressure is too high, eventually overflow out a vent on the roof. Old-Biscuit is right here... I wonder if the tank is vented inside, the tank vent collapsed into the FW tank, or there is some other leak or compromise of the tank.

[Old-Biscuit]

You will need to un-seal the dinette and access the tank so that you can check if tank is cracked, fill line leaks, overflow line is not connected, vent line leaking.

IF all connections are done right.....tank should NOT leak inside rig even IF you fill too fast..it should just burp back on you thru fill line.

As the contractor how to access the tank. Something is NOT correct.

[mich800]

I almost sounds like he vented it on the inside of the trailer. Not sure how else water would get anywhere but the tank or vent and fill port.

[Iowa_Cowgirl]

It somehow flooded the camper from under the dinette where the tank is located.
When I asked the contractor, he said it flooded because I filled it too fast.
While it also spilled out at the fill spot outside the trailer, it also flooded the camper part. I can't access the water tank because the dinette is sealed. 😞
Please advise.

[Pangaea_Ron]

We have a similar issue. The overflow tube seems to create a suction if the tank is over-filled, if we park on a hill, or if we are driving on a curvy road. You can search for this issue on this site, and the solutions seem to be: Plug the overfill tube, run a loop above the overfill tube, or create a vent at the top of the overfill tube.

I'm tempted to run a loop above the overfill tube with a valve that I can close when traveling, and open when operating the system. . . if I can remember.

[TucsonJim]

The tank is somewhat flexible on most units. When you're filling it up fast, the pressure from the hose causes the tank to bow out some. When you remove the hose, you can get a couple of gallons of splash back. It happens to me all the time, and is not a problem.

[brirene]

Since yours is a custom job its hard to know how it is set up. I will say that my Jayco fiver certainly has an overflow tube. As a matter of fact, that's how I know my tank is full. When you say you overflowed yours, how was it flowing? A tube, hose, or just emptying out of the bottom?

Edit: Biscuit's speed typing course paid off! Lol

[Old-Biscuit]

Where did it come out....back thru fill opening? IF so that can happen cause you are filling faster than tank can vent.

Also most fresh water tanks have an 'overflow' to ground.
That's how I know my tank is FULL :B

[DutchmenSport]

Your tank has to be vented somehow, otherwise, with the cap on the tank, you'd have a vacuum and nothing would pull through the water pump. What's happening is, you are either filling too fast and it's backfeeding into the vent and spewing out, or else your tank is really full and spewing out. Either way, slow the water down and see if you can fill more.