Free Water

Lynnmor wrote:

marcsbigfoot20b27 wrote:


That explains the physics of water gushing out on right hand turns when over 1/3 tank. Looks like orifice and or valve install coming soon.

So you want to take the chance of pressurizing the water tank? Find a way to route vents higher than the tank.

Tank at half full

No, that's why I want to block the vent line with a plug or valve that has a small ORIFICE in it to LIMIT the volume of water that flows out while still allowing it to vent and not overpressure.

I would rather it pizzle than pour.

marcsbigfoot20b27 wrote:


That explains the physics of water gushing out on right hand turns when over 1/3 tank. Looks like orifice and or valve install coming soon.

So you want to take the chance of pressurizing the water tank? Find a way to route vents higher than the tank.

Tank at half full

Well that explains it.....I just measured the top corner of the tank where the fill and vent hoses are to the vent on the outside................6"

WTF were they thinking?

That explains the physics of water gushing out on right hand turns when over 1/3 tank. Looks like orifice and or valve install coming soon.

JaxDad wrote:
I'm kind of confused about the concept of a water vent siphoning a tank dry.

In order for the vent to 'siphon the tank dry' there would have to be two things that I've NEVER seen on an RV.

First, the vent tube connected to the water tank would have to extend to the very bottom of the tank. They are merely attached to a nipple on the top of the tank, there is no internal component at all.

Second, the vent tube would need to extend to a point lower than the lowest point of the tank. I've never seen a vent that was even as low as the top of the tank, let alone the bottom.

You are right that draining a tank completely is not very common or even possible. However my trailer will drain it down to about 1/3-1/2 tank.
Regarding the tanks, many trailers have VERY short, but wide tanks, that are mounted directly under the floor. The connections are NOT always on top. Also, on my trailer (and many others) the vent tubes do indeed extend below the bottom of the tank.
Best bet, unless the underbelly is open, is to just put the shutoffs on the vent lines. I labeled my water fill cap and my water pump switch so I don't forget to open/close the valves.

JaxDad wrote:
I'm kind of confused about the concept of a water vent siphoning a tank dry.

In order for the vent to 'siphon the tank dry' there would have to be two things that I've NEVER seen on an RV.

First, the vent tube connected to the water tank would have to extend to the very bottom of the tank. They are merely attached to a nipple on the top of the tank, there is no internal component at all.

Second, the vent tube would need to extend to a point lower than the lowest point of the tank. I've never seen a vent that was even as low as the top of the tank, let alone the bottom.

You are correct, it is not a siphon. I have argued this at the factory and here, but if folks want to call it a siphon, fine. It is simply a spill, there are two holes at the top corner of the bucket and water spills out when the bucket is tilted a few inches or when it is sloshed that way in a curve. Of course the flow will increase once hose is full and gravity aids the outflow. I tried to explain this at the KZ factory but their engineers never took the "water runs downhill" class. Again there are tens of thousands of RVs out there with the same problem. I had water cooled brakes on one side and reported it to the NHTSA, but they are another useless agency. I watched as another KZ was being fixed at the factory and they just added a vent that ran uphill and left the spill hoses in place. Folks think that these things are engineered, yeh, right. Others manufacturers do the same dumb thing mainly because doing it right would add a few bucks to the cost.

JaxDad wrote:
I'm kind of confused about the concept of a water vent siphoning a tank dry.

In order for the vent to 'siphon the tank dry' there would have to be two things that I've NEVER seen on an RV.

First, the vent tube connected to the water tank would have to extend to the very bottom of the tank. They are merely attached to a nipple on the top of the tank, there is no internal component at all.

Second, the vent tube would need to extend to a point lower than the lowest point of the tank. I've never seen a vent that was even as low as the top of the tank, let alone the bottom.

Mine would not siphon dry, but at least 1/2 would go away. . .

When your boondocking and have no access to water once there, every gallon counts

I'm kind of confused about the concept of a water vent siphoning a tank dry.

In order for the vent to 'siphon the tank dry' there would have to be two things that I've NEVER seen on an RV.

First, the vent tube connected to the water tank would have to extend to the very bottom of the tank. They are merely attached to a nipple on the top of the tank, there is no internal component at all.

Second, the vent tube would need to extend to a point lower than the lowest point of the tank. I've never seen a vent that was even as low as the top of the tank, let alone the bottom.

The only time I leave without a full water tank is when I need to leave with the trailer winterized. In that case I fill the tank at a gas station when I get out of the freeze zone. I have never had a problem with a gas station letting me get water. I have my own hose, am buying gas, and offer to pay for the water. (I've never been charged for the water.)

Dump stations usually have water as well in the same general area. RV campgrounds will usually let you dump and fill the water tank for a small fee. It just hasn't been a problem.

RV's with two vent hoses out the bottom, usually have no gravity fill port and are pressure fill only.

A gravity fill is a cap that can open and water poured in, and have a vent next to the cap. We are not discussing this type.

The pressure fill type have a valve that you turn to direct water from the city water connection and send it to the tank. Air is expelled out the vent pipes that are all too often just straight out the bottom. Two pipes are used for redundant safety purposes. Plugging these vents, or using a "small hole" is not something you should do. The tank (which is not rated for pressure) can expand and do structural damage. Those vent hoses need to be routed correctly as I previously posted.

My tank now has both a gravity fill and pressure fill for convenience and safety. They are in a locking hatch with venting drilled thru the door.

My vent tube is above the water tank by a good foot or more.. I've never lost water out of it, or had it siphon the tank dry?

People do a lot of things I don't do and I do a lot of things other's don't do, so I guess it's just a personal preference thing..

I always leave home with a full water tank... Just never know what you are going to find at the other end. Each to their own I guess.

Happy Camping!

Mitch