fresh water tank overflow syphoning tank dry

[Goostoff]

Let me start by stating that my overflow in a tube sticking out the bottom of the underbelly of the trailer. I have always just filled my tank untill water starts to flow out of the tube. It would always drain off the little bit that got in before I could pull the hose. For some odd reason this year when i do this the water will sit there and keep running out and will syphon the tank nearly dry before it stops running. Anyone have any idea what is going on. I'm thinking about installing a valve on the end but I fear that I would forget to open it and make even more problems

[Lantley]

Lynnmor wrote:
I have been thru this too many times before. The reason that things never change is that too many have no idea how things work.

Is it up to the buyer to understand how to correctly pipe a fresh tank?
Do I need to submit my own drawings at time of purchase?

[STBRetired]

There is no way the vents/overflows (I have 2) on my fresh water tank could ever siphon water from the tank. They are attached to fittings on the top of the tank and do not have any hose that extends into the tank. They might drip a bit on acceleration, braking, and turns. At most, I would say I lose a quart or 2 of water. Never enough to actually be noticed when looking at the tank.

[Lynnmor]

I have been thru this too many times before. It took some effort, but I convinced a manufacturer that the stupid design allows water to spill out, and they then changed to venting above water level. The reason that things never change is that too many have no idea how things work. Water runs down hill, it does not jump up to the top of the tank to find a hose.

[Lantley]

Lynnmor wrote:

Lantley wrote:
My set up does not gravity fill. You can fill via a pressurized water hose or via a bucket using the on board pump. Filling is not a problem. I have a 80 gallon fresh tank,filling via gravity would be a PIA.
My overflow and vent tube both exit beneath the fresh tank.If you overfill the fresh tank a siphon will/can start. Once started the siphon can dump a lot of water on the ground.
iIhave resolved this issue by installing valves on my drain and siphon lines

We need to quit calling a spill a siphon. The vent hoses are attached at the top of the tank and go down towards the road. If the trailer is tilted, water can spill out. If you round a curve and the water sloshes to the vent side, it will spill out. A siphon requires that the hose extend down into the tank, but that is not how they are made.

Adding valves to vents is both a miserable way to deal with a water system, and major damage can happen if one ever forgets to open them.

The proper fix for this cheap factory shortcut is to route the vent hoses up and out well above water level.

It's a siphon because once the water starts to flow it does not stop.
It's not a simple matter of the water spilling out.
I I overfill my tank enough to get water flowing out of the vent /overflow lines a siphon will start and continue long after I have stopped water flow into the tank.
I agree if the lines were run above the tank a siphon would not start, however for many of us the lines come out of the underbelly and siphoning is possible.

[Lynnmor]

Lantley wrote:
My set up does not gravity fill. You can fill via a pressurized water hose or via a bucket using the on board pump. Filling is not a problem. I have a 80 gallon fresh tank,filling via gravity would be a PIA.
My overflow and vent tube both exit beneath the fresh tank.If you overfill the fresh tank a siphon will/can start. Once started the siphon can dump a lot of water on the ground.
iIhave resolved this issue by installing valves on my drain and siphon lines

We need to quit calling a spill a siphon. The vent hoses are attached at the top of the tank and go down towards the road. If the trailer is tilted, water can spill out. If you round a curve and the water sloshes to the vent side, it will spill out. A siphon requires that the hose extend down into the tank, but that is not how they are made.

Adding valves to vents is both a miserable way to deal with a water system, and major damage can happen if one ever forgets to open them.

The proper fix for this cheap factory shortcut is to route the vent hoses up and out well above water level.

[Lantley]

My set up does not gravity fill. You can fill via a pressurized water hose or via a bucket using the on board pump. Filling is not a problem. I have a 80 gallon fresh tank,filling via gravity would be a PIA.
My overflow and vent tube both exit beneath the fresh tank.If you overfill the fresh tank a siphon will/can start. Once started the siphon can dump a lot of water on the ground.
iIhave resolved this issue by installing valves on my drain and siphon lines

[maillemaker]

It might not be your only problem, if you would be able to see inside the fill hose, you might not like what is in there. I had a clear fill hose on a trailer years ago that I replaced several times because of mold.

Those vents that are not inside a hatch door will collect rain water, wash water, dust and just about anything. My opinion is that they should have never been certified for a potable water system.

My vent is inside the hatch door.

I'm sure the fill neck gets yucky, too, but it's black rubber so you can't see it. I suspect that it dries out well enough since it's so big in diameter. It's the little vent tube that stays damp.

The tank itself is clean (it's translucent so you can see it).

I don't worry about it though - we don't drink or cook with the onboard water. Just brush teeth. I sanitized the water tank once 10 years ago but have never done it since. I drain the entire system after ever trip.

[Lynnmor]

maillemaker wrote:
My RV has a vent integral with the fill neck. The air is expelled from a little hole right next to the big hole for the garden hose. Inside the RV there is a small clear plastic hose that runs from the top of the tank to the vent hole.

My only problem is mold grows in that tube.

Steve

It might not be your only problem, if you would be able to see inside the fill hose, you might not like what is in there. I had a clear fill hose on a trailer years ago that I replaced several times because of mold.

Those vents that are not inside a hatch door will collect rain water, wash water, dust and just about anything. My opinion is that they should have never been certified for a potable water system.

[camperdave]

Only way I could see the vent line (that used to vent correctly) becoming a siphon is if the vent hose got pushed further into the tank further than it used to be.

Any chance you can physically get to and look at the fill/drain/vent lines on the tank?

[maillemaker]

My RV has a vent integral with the fill neck. The air is expelled from a little hole right next to the big hole for the garden hose. Inside the RV there is a small clear plastic hose that runs from the top of the tank to the vent hole.

My only problem is mold grows in that tube.

Steve

[Lynnmor]

DutchmenSport wrote:


So, I guess what I'm asking, are you sure that tube UNDER the trailer is not the drain valve and the vent is somewhere else? I've never heard of having the vent tube 'below' the object it's venting, only above it.

Tens of thousands of RVs were/are produced with a pipe attached to the top corner of the water tank and then run out thru the bottom. No, they don't work, it is just a cheap way to get them out the door.

[Lynnmor]

Do you have a gravity fill where you just stick in a garden hose? Does it have a vent next to it? Are you sure that the pipe expelling water is a vent? Is the trailer sitting level? Do you have a means of pressure filling the tank with a garden hose attached?

[Hondavalk]

drsteve wrote:

DutchmenSport wrote:


So, I guess what I'm asking, are you sure that tube UNDER the trailer is not the drain valve and the vent is somewhere else? I've never heard of having the vent tube 'below' the object it's venting, only above it.

What he said.

What they said

[Bobbo]

Goostoff wrote:
Let me start by stating that my overflow in a tube sticking out the bottom of the underbelly of the trailer.

I have never seen an overflow (actually vent) tube anywhere except right beside the gravity fill port. If you have a fancy trailer with levers to flip rather than a gravity fill port, I have no idea.

[drsteve]

DutchmenSport wrote:
Normally, isn't the overflow pipe also the vent pipe? If you close off the vent pipe with a valve, wouldn't that cause a vacuum in the tank and then nothing would pump out with the on-board pump.

Most tanks have a drain valve and an over-flow/vent. The end of the over-flow/vent is usually placed higher than the top of the tank, and installed in such a way that the direction is always upward, never down. Down could cause a vacuum in the tank.

Even if your tank is siphoning, there has to be a secondary opening somewhere to prevent the tank from vacuuming up, unless when you disconnect the water hose and the air is coming from there. Now, if you fill is gravity fill, then it does have the secondary opening to allow siphoning to occur.

So, I guess what I'm asking, are you sure that tube UNDER the trailer is not the drain valve and the vent is somewhere else? I've never heard of having the vent tube 'below' the object it's venting, only above it.

What he said.