Fresh water siphoning problem

[Dragginourbedaround]

I have a 2011 Winnebago Vista 35F. When I fill the fresh water tank to capacity it pours out the overflow tube until there is about a third to a half a tank left. Winnebago says it's a siphoning problem and a dealer said the same thing but it was because pressure has built up in the fresh water tank and won't allow it to fill. At least that's what I understood from both conversations. Winnebago said I had to bring it to a dealer to get it fixed and the dealer said to just empty the tank and let it sit empty for a while and that should eliminate the pressure. I've emptied the tank and letting it sit overnight. The dealer also thinks there should be a gravity feed somewhere that I could open and that would relive the pressure, but I can't find one. Has anyone else had this problem? Any thoughts?

 

[Alfa38User]

Many have had that problem but not necessarily on a Vista. The problem often occurs because the vent tube was placed too low on the tank or it loops outside the tank to a lower position and fills with water. Once it fills and starts leaking (siphoning) out, it won't stop until it the tank end is once again above water level in the tank.

Best to find a dealer who is willing to solve the problem by fixing the vent tube properly, and assuring it is not looping too low after leaving the tank before actually reaching the vent outlet. It may require the installation of an anti-siphon device in the line... Or drop in at Winnibago factory service.

The one thing it is not is a pressure buildup in the tank but it is the result of a water filled vent connection. Many coaches no longer have a gravity fill port.

 

[carson]

Only one thing I can think of.

  If you completely fill the tank there will be pressure building up  and force water out the siphon hose.  Once it takes over it will keep draining water until the bottom of the hose sucks air.

  An easy test would be to only fill the tank to, let's say 3/4 full, before pressure builds up and forces the water to drain.

Certainly it could be that the hose is a little too low; certainly not worth spending big bucks on having it fixed.  Give it a try...it's not a major problem.

 

[Dragginourbedaround]

An easy test would be to only fill the tank to, let's say 3/4 full, before pressure builds up and forces the water to drain.

Thanks Alfa38User.

Carson: I'll give that a try, thanks.

 

[carson]

BTW, I have seen many RV's going down the road  dripping/spewing water. Probably the same situation.

 

[John Canfield]

..The dealer also thinks there should be a gravity feed somewhere that I could open and that would relive the pressure, but I can't find one. ..

To save a few bucks, Winnie stopped installing gravity fills on some models for some model years.  I let them know that I thought that was a terrible product planning decision because there are some non-commercial campgrounds where the only way you can fill a tank is via the gravity fill.

You most certainly have an issue of some sort with the tank vent - not installed, kinked, looped, who knows what.  Get your dealer to investigate - Winnie pays the dealer's going labor rate for warranty work so there should be no pushback from the dealer about spending the time to properly investigate your issue.

 

[Quillback 424]

I had this happen when I would fill my tank until it would overflow and then shut off the water supply. Since I can see my tank from a compartment on the opposite side, I now fill to about one inch from the top of the tank and then walk around and shut off the water. No more problem.

 

[Garyk]

I had the same problem with our Vista 35F, the fix for me was. Installing a shutoff valve on the overflow pipe that passes thru the wet bay. Got one from Loews that fits over the overlfow pipe which I believe is 3/4" pex. I leave the valve open most of the time unless I need a full tank...
Its not a pressure problem, the tank simply siphons out.....lousy design is what it is...how can the tank get pressurized with a 3/4" vent pipe??
I had filled the tank once to where the gauge read full, this is only about  a little over 2/3 full after I looked at the tank and it still siphoned once I drove a few miles....

 

[afchap]

I have experienced siphoning a time or two when traveling w/a full tank (rare situation .. why carry all that extra weight if you don't have to?). I found that if I fill the tank to the overflow point, and then pull the tank dump valve for 30 seconds or more, that will break the siphon and I won't lose water.

 

[driftless shifter]

I have experienced siphoning a time or two when traveling w/a full tank (rare situation .. why carry all that extra weight if you don't have to?). I found that if I fill the tank to the overflow point, and then pull the tank dump valve for 30 seconds or more, that will break the siphon and I won't lose water.

Brilliant and elegant solution.

Bill

 

[Dragginourbedaround]

I tried Carson's solution with a half tank and it seems to be working. I'm going to try afchap's with a full tank.

Thanks everybody.

 

[Rene T]

and then pull the tank dump valve for 30 seconds or more, that will break the siphon and I won't lose water.

AFCHAP,
Bear with me. I'm confused which doesn't take much!!!!  What are you calling a dump valve? When I hear someone say those words, all I think of is the valves for the black and gray water tanks. When you say dump valve, are you referring to the small drain valve that's used to drain the tank?

 

[John Canfield]

.... When you say dump valve, are you referring to the small drain valve that's used to drain the tank?

Paul is referring to your fresh water drain valve.

 

[afchap]

Yes. My freshwater "drain" is operated by a T-handle in my water compartment right beside the black and grey water dump handles.

 

[Al Todalen]

Please reconsider the use of a shut off valve in the overflow line. It's a major problem just waiting to happen. If you get distracted and forget to open it prior to filling you risk damaging your tank from the unvented pressure. Conversely, when you arrive at your destination if you forget to open the valve you risk collapsing your tank as water is used. I tried that approach myself initially and  found that I did in fact forget to open the valve a couple of times. I removed the shut off valve in the overflow line after that.  What i did to prevent siphoning was to permanently relocate the bottom of the overflow line above the height of the water tank. Any overflow while filling dribbles into the into the wet bay and causes no harm. I've also seem to recall that others have had success by contacting Winnebago and they had a dealer change the overflow line configuration to include a loop well above the tank height. 
Happy trails,
Al

 

[carson]

I had the same problem with our Vista 35F, the fix for me was. Installing a shutoff valve on the overflow pipe that passes thru the wet bay. Got one from Loews that fits over the overlfow pipe which I believe is 3/4" pex. I leave the valve open most of the time unless I need a full tank...
Its not a pressure problem, the tank simply siphons out.....lousy design is what it is...how can the tank get pressurized with a 3/4" vent pipe??
I had filled the tank once to where the gauge read full, this is only about  a little over 2/3 full after I looked at the tank and it still siphoned once I drove a few miles....

I am surprised that no one commented on the posters declaration.

The fresh water tank is a sealed system... not open to outside intrusion of bad stuff.

The only opening is the overflow tubing, usually a small flexible tube with a bug-filter at its end.

 

[Lou Schneider]

I have trouble seeing how a freshwater tank can siphon through it's vent, since the vent outlet is as high or higher than the top of the tank and in any case the tank end stops within a half inch or so from the top of the tank.  Once the ank tend is out of the water any siphon is broken, so there's no way a short tube can siphon the tank to the 1/2 or 3/4 level.

I think what is really happening is centrifugal force during turns and normal road motions driving down the road is sloshing the water in the tank, so the peak of the wavefront is higher than the vent tube, making water flow out of it.  Do this often enough and you can drain the tank well below the level of the vent.

The solution is to loop the vent tubing high enough so the displaced water doesn't reach it.  If you don't have vertical clearance, loop the vent line across the length of the tank to the opposite end and back.  This way, no matter which way the tank sloshes, part of the line remains above the water level and stops the water from draining out.

This is different than overfilling the tank.  In this case the tank will distend and water will flow out of the overflow until the tank contracts back to it's proper shape.

 

[Al Todalen]

I have trouble seeing how a freshwater tank can siphon through it's vent, since the vent outlet is as high or higher than the top of the tank and in any case the tank end stops within a half inch or so from the top of the tank.  Once the tank tend is out of the water any siphon is broken, so there's no way a short tube can siphon the tank to the 1/2 or 3/4 level.

Lou, at least in my case,  it would start to siphon immediately if I filled the tank enough to get water flowing out of the overflow/vent. It would then continue until I only had about 2/3's of a tank remaining. We boondock a lot and I like to fill the tank to it's utmost. On my unit the overflow/vent extended vertically several inches below the tank where it terminated with an insect screen. I have no idea how far it goes down inside of the tank but I suspect it's about 1/3 of the height because that's about where it quits siphoning. Also keep in mind some tanks are rather shallow and their volume is spread out over a larger area than others so a couple of inches can be a significant amount of water. My 75 gal tank is only 7 inches high and 1/3 of that capacity equates to loss of 25 gallons. As I said, raising the terminus (insect screen end) of the overflow/vent above tank height solved my problem.
Happy trails,
Al

 

[lumpy75]

I have a Columbus fifth wheel and have had this issues as well when full filling the tank. Also had it a time or two with a Coachman trailer. Lots of god ideas will have to try them. When dry camping last year at Taladaga I found I had lost about 1/3 of the tank which cost me $20 to fill the tank later. I was thinking of trying the fill till full then drain till the overflow stops and see if that works. I like the idea of putting a valve on it but the forgetting to open could be an issue. Not saying I forget things butttt.

 

[Jim Godward]

Here are 2 approaches to solving the overflow problem.