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Old 05-13-2015, 10:32 PM   #21
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Originally Posted by Peter27C View Post
Here is a pix of my extended overflow pipe.Attachment 94148
That picture is worth a thousand words.

Thank you very much.

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Old 05-14-2015, 05:51 AM   #22
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Looks like there is a tight fit between the tube out of the top of the tank & the drain tube & it would be difficult to get to it to just cut it off & install a larger drain tube without the tight fit. So for me, the solution is to just not fill the tank all the way until I find a reliable service center that can modify it with the extra coil of tube on top.
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Old 05-14-2015, 05:57 AM   #23
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A the problem is not siphoning at all. For it to siphon the overflow pipe would need to go down into the tank which it does not. We know this because the gravity feed pipe is below the top of the tank, as seen through the open locker on the RH side of the coach, so if the overflow pipe also went below the top of the tank air would be trapped there and the tank could not be filled to the top.
The problem is that the tank goes the full width of the coach, the overflow pipe is barely an inch above the top of the tank so if the left hand side of the coach is lower than the right, the water just runs out. When you drive around a corner the water sloshes back and forth and also just flows out.
Putting a tap in the overflow will work but it has to be up above the larger piece of pipe that has been screwed onto the short overflow pipe, and you have to remember to turn it on and off.
See the picture above, by raising the U bend of the overflow pipe up, the lowest point is now the door on the gravity fill on the RH side of the coach so the tank can know be filled to that point, and the water does not drain out the overflow anymore because it is higher, but air can still get out when filling (and in when water is being used).
Extending the pipe took about three quarters of an hour, all done in a Home Depot car park! It is not a hard job.
The coil on laying on top of the tank won't work properly either if the coach is parked left side down as the water will still flow down hill. It would reduce the cornering effect, but would probably take not much less time to do than doing the job properly.
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Old 05-14-2015, 06:11 AM   #24
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If you can see/find the top of the overflow pipe (the highest point) drill a tiny 1/16 inch hole in the to of the pipe/tube, It must be above the highest water level. Water will not escape out of the hole if its at the highest point, but the small hole will provide enough air venting to break the siphon.

(we do this on aircraft fuel tank overflow vent tubes)
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Old 05-14-2015, 08:17 AM   #25
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It's not siphoning!
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Old 05-14-2015, 08:57 AM   #26
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I agree with Peter27C it is not siphoning. The attached picture is on the inside of the tank. The overflow/vent is attached with a spin-weld fitting on top and the elbow in attached to the top. There is nothing protruding into the tank.
Need to get the overflow/vent loop higher. Drilling a hole in the elbow will allow water to leak out when you turn to the right.
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Old 05-14-2015, 09:51 AM   #27
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It's not siphoning!
I may agree with you on the gravity feed rv's as long as the fill cap allows air to flow back and forth.

Those that do not have gravity feed and are losing close to what appears to be quarter tank or more it is siphoning. I had this problem with my 2012 vista. I could over fill it full on a level lot, turn the hose off and watch it siphon out around ten gallons of water. The units that have no gravity feed (and yes they do exist) have no way to allow air to get introduced into the top of the tank. On my vista where the overflow came out of the tank I replaced the elbow with a tee and simply vented it above the tank. Ended up only losing a few gallons when driving due to the sloshing effect but never lost the ten gallons I seen before.

For those that are losing around ten gallons and have gravity feed, try removing your fill cap. If you don't lose the massive amount of water you will know if it is siphoning or just sloshing out the overflow tube.
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Old 05-14-2015, 10:21 AM   #28
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If you can see/find the top of the overflow pipe (the highest point) drill a tiny 1/16 inch hole in the to of the pipe/tube, It must be above the highest water level. Water will not escape out of the hole if its at the highest point, but the small hole will provide enough air venting to break the siphon.

(we do this on aircraft fuel tank overflow vent tubes)
I don't think that this is a good idea for this application. If you could guarantee that the drilled hole was always above the water level; then fine, but this is not the case.

In my case, my driveway is long and steep uphill and the street that I live on slopes mildly uphill for 1/4 mile. Since the overflow is at the back of the tank, gravity takes over and water flows out. There is some siphon effect as long as the water is at the level of the overflow but it is mostly gravity. I could lose a lot of water this way. Had I drilled a hole in the overflow, I would have some water in my storage compartments and still lost water out the overflow.

I went with a positive shut off valve. Others have used a 'dribble' valve which I think is a better idea.

I leave home often with a full tank because my destinations often have no water available. When filling my tank, the valve is open, at all other times closed. I have used this setup for 7 years with no issues.
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Old 05-15-2015, 04:39 AM   #29
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I don't think that this is a good idea for this application. If you could guarantee that the drilled hole was always above the water level; then fine, but this is not the case.

In my case, my driveway is long and steep uphill and the street that I live on slopes mildly uphill for 1/4 mile. Since the overflow is at the back of the tank, gravity takes over and water flows out. There is some siphon effect as long as the water is at the level of the overflow but it is mostly gravity. I could lose a lot of water this way. Had I drilled a hole in the overflow, I would have some water in my storage compartments and still lost water out the overflow.

I went with a positive shut off valve. Others have used a 'dribble' valve which I think is a better idea.

I leave home often with a full tank because my destinations often have no water available. When filling my tank, the valve is open, at all other times closed. I have used this setup for 7 years with no issues.
Reading all the comments & suggestions of others & from my personal experience so far, I agree the problem is primarily the sloshing of the water causing it to overflow through the tube, although I also believe it can siphon with a full tank & the MH sitting with the left rear low. I want to install a valve as you did & use it exactly the same way. Most of the time it will remain open because we only fill our water tank half way. But when we anticipate dry camping, I will fill the tank almost full & close the valve until we are to a camping spot where we will use water & then I will open it to prevent a suction building up as we use water (because we do not have a gravity fill).

I would appreciate any information about what kind of valve to install. What is a "dribble valve"? Does that relieve suction pressure without having the valve open?

Thanks,
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Old 05-15-2015, 09:34 AM   #30
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I would appreciate any information about what kind of valve to install. What is a "dribble valve"? Does that relieve suction pressure without having the valve open?
No idea what a dribble valve is but you can goto the local hardware store and get a press on valve to put on your overflow line. Sharkbite is brass version but others make a plastic version. You simply cut the overflow line where you want the valve and press the valve into the lines. Easy install.
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Old 05-15-2015, 10:05 AM   #31
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I would appreciate any information about what kind of valve to install. What is a "dribble valve"? Does that relieve suction pressure without having the valve open?

Thanks,
Cass
A dribble valve is one that does not completely shut off in the off position, a small amount of water will continue to flow. They are normally shower shutoffs that you see in the plumbing section of hardware stores. I am told that the dribble is to prevent scalding when it is turned back on.

If suction is the problem, this would relieve it. If gravity is the issue, this would minimize the problem as a smaller amount of water would flow.

Keep in mind that for the overflow to function as an overflow, the valve must be open.

Most motor homes use PEX and fittings are widely available. I used a positive shut off and located it so that I could easily reach it.
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Old 05-17-2015, 09:55 AM   #32
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Inquiry to Winnebago...

Considering all the varied input regarding this topic I have now posted an inquiry directly to Winnebago Industries about losing water from my fresh water tank.

Will post their response upon its receipt.

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Old 05-17-2015, 10:12 PM   #33
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Poster #6 posted a picture and I poster #7 indicated that I e-mailed WBGO and got the same picture posted in #6. Maybe you'll get another answer. Maybe if enough people question them they will do something about it.

I checked my unit a 2014 Vista 30T and my overflow tube is already a 3/4" pipe. There's not loose area at the top to allow air to break any siphoning that might occur. I'll also agree with Peter when he says unless the inside tube goes down into the water siphoning won't take place for very long once you get moving. I'm really not to sure exactly what to do at this point except to go to BED Good night!!

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Old 05-17-2015, 11:39 PM   #34
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This is the reply I had from Winnebago.......

David,

If the fresh water tank is overfilled it will create a siphon which will continue until the siphon is broke. I would suggest making an appointment with an authorized dealer for warranty repairs. In the meantime try filling the tank to around 90-95% of full capacity until your dealer can get you in for service.
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Old 05-18-2015, 12:06 AM   #35
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Imagine one of those cheap 5g collapsible water containers is your water tank in your rv. Now with the spigot at the top of the container on a table hook up a hose and extend it a few inches below the container. Suck on the hose to start siphon. Watch the container shrink as it expels water. At some point it can no longer expel water and that is the point the siphon will break, at that point the container will suck back in some air and the water level in the container will be quite low. That is what is happening to fresh water tanks. The plastic is much more ridged but it does flex with the weight of water. Only true way to fix it is to have air vent above the top of the tank. Btw, from the tanks I have seen the overflow connection is on the side of the tank, not at the top which makes this siphon issue even more common.
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Old 05-18-2015, 04:39 AM   #36
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This thread has become like ground hog day! I am struggling with what is still being written here, when the answers have been posted. Look up siphon in the dictionary. Look at post #6 showing how Winnebago built the water tank. See in the left hand detail, the half inch U section is stuck on the top edge of the tank and curves over the edge of the tank. The detail shows that just below the top of the tank a piece of 3/4 pipe is fitted over the 1/2 inch pipe and goes straight down and is held on with a screw. post #26 shows a pix of inside the tank, yes I know it's computer generated, but confirms the fitting does not descend into the tank, hence no siphon action can take place. The post #6 drawing is exactly how my RV water tank is assembled. I know this because I pulled this stuff of the tank to raise the height of the U bend.
Putting a valve on the 3/4 pipe won't fix the water running out of the tank because the 3/4 pipe is not sealed to the 1/2 inch pipe.
I doubt if anyone's RV is built different to Winnebagos drawing, but maybe this is the latest drawing and there are earlier versions of built. (Or maybe the boys brought some parts from home and built your RV different from the plans).
As I said in my post #23, I raised the U bent in a Home Depot car park while I was on the road so it's not too difficult, see the end result in post #18.
I removed the floor of the bathroom cupboard which is just held in with a few screws, drilled a pilot hole up from underneath then drilled back down from inside the cupboard. I assembled the U to get the spacing then drilled the second hole the required distance from the first. I will confess here that I used a Home Depot crimping tool to do the crimps.
Now when I fill the tank the overflow still lets the air out but the U bend is high enough that when the tank is full no water leaks out the overflow. And none flows out when parked on an angle or when driving round corners.

I accept I have been quite blunt in this post but people read these things looking for good information and it frustrates me to think someone would go the the effort of fitting a tap on the 3/4 pipe or what ever based on what they read here, only to find they have wasted money and time on what they thought was good information from a "trusted" site.

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Old 05-18-2015, 08:55 AM   #37
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I know I have a different system but looking at the pictures of the gravity fill door on the right side of the RV why don't you put a piece of scotch bright pad cut it to fit that whole area under the door and that should break up the vacuum effect on the tank. I mean just a thought and cost less then a dollar to try.


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Old 05-19-2015, 09:55 AM   #38
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Pete,

Read post 34, they called Winnie and they told him that if you fill it all the way it will siphon, right from the mfg. Just cause the over flow is at the top does not mean siphon cannot occur. If you fill that tank all the way to the top there is a good chance no or little air is in the top of the tank. That tube bends over just like you say, not sure on how far down that 1/2" tube goes and how that 3/4 tube is installed (in assume it terminates a inch below the 1/2" pipe). but let's say it goes down by 2" from the top of the tank as that is the way it looks in the picture. Once you top the tank off and force water out the overflow tube siphon has begun, it will continue until it reaches the end of the 1/2" tube. The tank will start to bow in (and this what I feel Winnie has not accounted for) as when siphon starts to occur no air can get into the top of the tank. This will continue until a point where the tank can let no more water out, then siphon will be broke and air will return to the inside of the tank. This will cause the tank to bow back out and the water level will now be lower than the end of the 1/2" overflow pipe. If you can't grasp this I suggest you get a collapsible water jug and try it at home. You can put the spigot of the jug at the top, run the overflow tube down a quarter of the way and start the siphon, you will see it end at that level, heck I bet if you used a hard 5 gallon water jug you could replicate the sidewalks of the jug expand and collapse.
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Old 05-19-2015, 05:06 PM   #39
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Hi Zman, just because the manufacturer calls it a siphon doesn't make it so, although I guess the first 1/2 inch of flow could be called that. By definition the word refers specifically to a tube in an inverted 'U' shape which causes a liquid to flow upward above the surface of a reservoir, with no pump but powered by the fall of the liquid as it flows down the tube under the pull of gravity, and discharging at a level lower than the surface of the reservoir whence it came. Note that while the siphon intake tube must be below the surface of the liquid in the higher reservoir, it need not touch the liquid in the lower reservoir and indeed there need not be a lower reservoir; a siphon can discharge into mid-air so long as the exit is below the surface of the upper reservoir.

It was their poor engineering that caused the problem in the first place. What I was trying to point out is that the fix is to raise the elbow, a simple job, and that shaging around with taps etc, or putting a coil of hose on top of the tank will not fix the problem properly
At the end of the day, with 40 years of engineering experiance, I came up with a simple fix that works.
If someone wants to put a tap on their line or a coil of hose on top of their tank, that's up to them. I just did not think it was right for people to read it here and then spend effort and money thinking it was an intelligent solution.
But debate is what makes life interesting, especially if it is based on experiance.

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Old 05-19-2015, 10:41 PM   #40
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Good stuff here...
Keep in mind that the top of the tank and the "u" has no access to air to move freely in and out of the tank, so the overflow going out the top of the tank is one leg of the u, then it goes across and then down completing the u shape. When you overfill the tank the pipe coming off the top of the tank has water in it and that level could be considered part of the reservoir. As water is being sucked out of the tank the tank compresses and that causes the water level remains the same. If Winnie had put a vent to air at the top of the overflow tube siphon would not occur, this is how I fixed my 2012 vista from dumping nearly 10 gallons of water.

I do agree with you on the coil stuff as well as a valve on the overflow tube on Winnie 30t mentioned in this thread if it is connected on this 3/4 extended pipe configuration, assuming there is a air gap between it and the 1/2" tube coming out of the tank. Keep in mind other rv's also have this issue and they may be reading this thread and a valve would work on the overflow tube although this is not my preference to fix the issue.
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