If I fill my water tank to the top it always starts to drain out of the overflow once I start driving wasting a few gallons of water until it stops. These few gallons of water can add up to enough water to wash a bunch of dishes, etc. I was told to add a coil of hose up on top of the tank so this may help prevent the so called siphon effect. Has anyone solved this problem. My 97 Adventurer would do the same thing.
Water Tank Overflow
- Thread starter 530ktm
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Rene T
Site Team
I think what may be happening is that the overflow pipe is sticking down in the tank a little and once it starts running out, it will start syphoning until the water level reaches the end of the pipe. If you can get to the top of the tank, try pulling the vent out a little. Another way is to put either a valve or a cap on the end of the vent. If you do that, you have to be very careful when you want to fill the tank. The pipe must be open to properly vent.
SargeW
Site Team
I had to put a shut off valve on a 5ver that I had. I would lose 1/4 tank of water due to siphon. I would fill the tank with the valve open, close the valve when it started to run out. Get to my location and open the valve. Use tank as usual.
You can also lose water if you're parked on a side slope. We once lost about a quarter tank of fresh water waiting to get into an FMCA convention parked on the side of the road because the vent outlet was lower than the top of the water tank.
afchap
Well-known member
When I fill my tank to the overflow point it will siphon out while driving. BUT, if I will open the fresh water drain for apx 30 seconds, that breaks the vacuum and the water does not siphon out.
Rene T
Site Team
afchap said:
Paul, I think what is actually happening is that you're lowering the water level below the vent pipe. If that vent pipe ran all the way down to the bottom of the tank, it would siphon all the water out of the tank.
afchap
Well-known member
That SOUNDS reasonable, but if I don't let that tiny 30 seconds of water out of my 100 gallon tank I can lose 60-70 gallons. After letting out that tiny amount, there is no loss. I know that does not make sense, but the fact that many have experienced it has been discussed quite a bit in the past. Once the siphon/vacuum gets started how much water can be lost defies logic.Rene T said:
Rene T
Site Team
I was thinking that if there was a vacuum in the tank it would have the tendency to stop the syphoning action. I don't know now. 
??? : :-\
??? : :-\Well I angled the vent pipe back a bit so it is not straight down and added about 5 feet of hose that goes up a good 4 inches above the tank and looped it around and then back out the drain tube. I filled my tank to the top then put the jacks down on the right side which shoved all the water in the tank over to where the vent is and nothing came out, zip. Last time I filled the water tank I went to Costco for gas and proceeded to drain a quarter of my water going and it continued while at the pump. I had to put the jacks down on the left side to raise up so the water level would go down and it then quite running out. I felt kind of silly wasting all that water and the attendant had to mop up the ground to get the water off. Anyways, it appears that this fixed my situation for now.
Rene T
Site Team
It sounds like you have easy access to the top of the tank. Can you try and pull the vent out of the tank a little?
Lou Schneider
Site Team
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- Mar 14, 2005
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It's actually centrifugal force during turns and the normal the side to side motion that "siphons" water out of the tank.
As you go around a corner, centrifugal force "tilts" the tank, making the water run to the outside edge. If that's where the tank vent is located, water spills out of the vent hose.
You can stop this by putting a vertical loop in the vent hose, so the high point stays above the water as it's pushed towards the outside of a turn.
Or you can run the vent hose across the width, on top of the tank and back. This way, the part of the hose on the inside of the turn stays "above" the water line and blocks it's escape.
As you go around a corner, centrifugal force "tilts" the tank, making the water run to the outside edge. If that's where the tank vent is located, water spills out of the vent hose.
You can stop this by putting a vertical loop in the vent hose, so the high point stays above the water as it's pushed towards the outside of a turn.
Or you can run the vent hose across the width, on top of the tank and back. This way, the part of the hose on the inside of the turn stays "above" the water line and blocks it's escape.
This is kind of what I did when I say the hose went up and put a loop on top of the tank and then back to the drain tube. As mentioned, I tilted the coach way over with a full tank and nothing came out of the vent so I believe this works.Lou Schneider said:
Clay L
Well-known member
Rene T said:
On Winnebago's the overflow fitting is spin welded to the top of the tank and doesn't extend into the tank at all.
What seems to be happening is that the tank expands quite a bit because the vent is too small and then when it overflows the water continues to flow until the tank relaxes to it's proper size and the vacuum formed matches the atmospheric pressure. That can result in a fair amount of water loss.
I think that is why opening a faucet as afchap said works.
Clay L
Well-known member
Lou Schneider said:
That is part but not all of the problem. On mine water will continue to flow out of the overflow tube when stopped. Adding a upward loop as you suggested did help the sloshing issue. See my post to Rene for the other part of the issue.
Daffy
Well-known member
Had this problem arise on my new to me coach primarily when turning left. Went and got a 1/2" inline pex shutoff and installed it on the single down tube overflow/vent. took all of 2 minutes to install and 20 seconds to walk back and turn off or on as the case needs to be so I don't damage anything or continue to lose fresh water.
Hated to add another step in setup or takedown but hey.. it works as designed..
Hated to add another step in setup or takedown but hey.. it works as designed..
DickHutchings
Well-known member
This is ridiculous. I can't even fill mine to the top. I've had TTs for years and none of them had overflows on them. Now I have a Winnebago and I have to relearn how to use the fresh water tank. I want to fill it completely and still have my precious water when I arrive at my destination. If I can get at the overflow I will find a way to block it until I get to my destination.
ennored
Well-known member
This has be talked (and argued) about quite a bit over the years. Winnebago implemented a change in the overflow line a few years back that breaks the siphon. There's a picture of Winnebago's solution in post #11 in this thread: http://www.irv2.com/forums/f101/fresh-water-tank-overflow-130344.html There's link to my fix in post #8.
