Fresh water tank overflow

[Norcalrv1]

I may have a partial solution. Yes agoutdoors I have the same issue and it has going on for a year.
Here is what I may have discovered.

When you fill an RV water tank you fill it, remove the fill hose and then turn your valves to do what ever you are going to do, such as, run from the water tank with the water pump. We have been doing that forever; that is how things work. Until now.

If my theory is correct about creating a vacuum with the water hose screwed into the fill valve as it is on these units, then this may fix the problem. Today I filled the fresh tank using the gravity feed system where the water pump actually pulls water from the storage tank in my truck to the water tank on the 5th wheel. When the water ran out the overflow I turned off the pump (could turn off the city water faucet if you are hooked up to it) and then turned the valves to the desired setting (in our case to feed from the water pump) and then and only then remove the hose that is screwed into the 5th wheel the water should stop running out of the overflow. And, you what-it worked. The question of course is can we get the water pump to pump water to the inside faucets. So far, yes. My tank, however, only read full for a very short time. Obviously the sensors are in the wrong place. So far this seems to be the answer to one issue. I don't see any harm since the overflow vent is open to the atmosphere-at least I think that is. No guarantees here.

When I was getting water today I was discussing this with a gentlemen from Michigan. He and others that he knows leave with a full tank and arrive with less than a full tank. He said that the water siphons out while you are driving. So what they do is clamp off the overflow line and that stops that. He said that you must remove the clamp before getting water from the tank or you will collapse the tank. He has had rigs that siphon and ones that don't. I have never had one that did before this. Good suggestion.

Let's keep working on this and see where we get.
Rod Zebb
Fairfield, CA
2014 337 RLS
2014 RAM 3500

[Cate&Rob]

To drain 15 gallons, the overflow tube somehow must end up several inches under water inside the tank. This is more than tank wall flexing or fill valve pressure/vacuum would account for (in my opinion). In boats, we use high hose loops with vacuum breaks to prevent essentially this same thing from happening. Of course, in this instance we are trying to keep the water out . . . not in . See my earlier post.

Rob

[Norcalrv1]

Rob, I agree with you. Sometimes the flow is extensive, sometimes not. There is just no pattern to it. Why the difference, I have no idea. Gets kinda of old after a year of no answers. Seems like others are having the same problem.
Thanks for your input.
Rod

[Retread68]

When the temp warms and I can work on my 303 it seems the undercarriage barrier will be coming off so I can see how things are put together. My previous 5er did not have a "kant-leak" valve and it did not leak nor did the fresh water tank have any excess overflow losses. That FW Tank had a spun-in fitting on the top of the tank with a clear 3/8" tube connected, going from there to the vent outlet of the fresh water fill / city water connection. The fill / connection were higher than the top of the FW Tank, thus no siphon effect could occur.

IF the overflow tube on the 303 extends into the tank with the outflow termination point being below the tank then a siphon effect could occur. If this is the case I will install a double airlock chamber with PEX that rises above the tank and then down, which should stop all siphon actions. Again - I don't know what is there until the undercarriage is opened.

[Norcalrv1]

It will be interesting to know what you find out. You are right, there is no overflow at the vent on the valve where the water goes into the tank. My previous rigs had them and water flowed out when the tank was full. I also have never had a siphon effect before. My solution at this time is to not let any air enter the hose connection and things are working ok. Maybe not correctly, but the massive overflow when I fill the tank has stopped. Seems like you have the solution.
Rod Zebb

[agoutdoors]

Keep in mind, I was seeing water running from the underbelly prior to me ever putting water in it. I only put water in it a few days ago when I picked it up from the dealer after some major repairs were completed (took 50 days to do)
So, since the dealer said they looked in the underbelly and "found no signs of water - no water trails", etc..., I decided to look myself. First - I am pretty sure the dealer didn't make any effort to look. All the factory rubber silicone was still in place around the suspension mounts, water drain, septic drain pipe, etc... Second - there was a fair amount of water in the underbelly and some of the insulation was soaked. I took pictures and some videos of the water running out from the underbelly and also from the insulation when I removed it and hung it up. I have dropped as much of the rear belly plastic cover as possible but am not able to remove it completely with out cutting it in places or removing hardware from the rig. I have also pulled out the insulation. I did note that there appeared to be more moisture between the plastic underbelly cover and the thermal barrier that is underneath.
I ran water in different places in the rig but didn't see any signs of new water running anywhere.
The only thing I can't test at home is adding water to the system since my well is not fit for drinking or storage and don't want to contaminate my 5th wheel tank and lines.
At this point, I can't tell why there is water under there. I also noticed a little bit of moisture in the front underbelly (a little insulation was wet) and again between the plastic underbelly cover and the thermal barrier there was a lot more moisture (I only pulled a few feet of the front one down but stuck my head in from the back area).
Once I transfer my pictures and videos from my phone, I will try and post a few here.
My plan is to call GD on Monday and see what we need to do to resolve this. Our first camping trip was planned for this coming weekend so that is up in the air.

[agoutdoors]

I may have a partial solution. Yes agoutdoors I have the same issue and it has going on for a year.
Here is what I may have discovered.

When you fill an RV water tank you fill it, remove the fill hose and then turn your valves to do what ever you are going to do, such as, run from the water tank with the water pump. We have been doing that forever; that is how things work. Until now.

If my theory is correct about creating a vacuum with the water hose screwed into the fill valve as it is on these units, then this may fix the problem. Today I filled the fresh tank using the gravity feed system where the water pump actually pulls water from the storage tank in my truck to the water tank on the 5th wheel. When the water ran out the overflow I turned off the pump (could turn off the city water faucet if you are hooked up to it) and then turned the valves to the desired setting (in our case to feed from the water pump) and then and only then remove the hose that is screwed into the 5th wheel the water should stop running out of the overflow. And, you what-it worked. The question of course is can we get the water pump to pump water to the inside faucets. So far, yes. My tank, however, only read full for a very short time. Obviously the sensors are in the wrong place. So far this seems to be the answer to one issue. I don't see any harm since the overflow vent is open to the atmosphere-at least I think that is. No guarantees here.

When I was getting water today I was discussing this with a gentlemen from Michigan. He and others that he knows leave with a full tank and arrive with less than a full tank. He said that the water siphons out while you are driving. So what they do is clamp off the overflow line and that stops that. He said that you must remove the clamp before getting water from the tank or you will collapse the tank. He has had rigs that siphon and ones that don't. I have never had one that did before this. Good suggestion.

Let's keep working on this and see where we get.
Rod Zebb
Fairfield, CA
2014 337 RLS
2014 RAM 3500

If I understand you correct, I have always filled my fresh water tank by running until it overflows, turn the water source off, then remove the hose - is that what you were referring to? The other day when I filled it up it seemed to run for a long time after shutting the water off.

[agoutdoors]

To make this theory viable requires another way for air to get into the water tank. Is this what the "vent" opening in the lower right of the Anderson panel does ?

Attachment 1473

I pulled the access panel off my 385TH and that vent hole serves no purpose...its just open on the other side with nothing attached. The vent hole is shown just below one of the connections.

[dirtclod]

On previous rv, we installed a valve on overflow line to keep from losing (from sloshing ) water going down the road. When we reached destination, opened valve. Does overflow line protrude below belly? I am curious what GD thinks or what the reply is ???

[Norcalrv1]

If you have water in the underbelly and you have never put water into the tanks, you may have a leak somewhere. It always rains in Washington and it may be rain water leaking around a slide or seal somewhere. I can not think of any other reason why you would have a water in the belly if you have never put water into your tanks.
Good luck figuring this one out. Glad that you got your other issues fixed.
Rod