Filling fresh water tank, Siphons out??

bowtie_guy · 06-15-2015, 03:41 PM

The other day I went to fill my fresh water tank for my trip. I put it on then started to do other stuff. Noticed water coming from the overflow/vent line next to the drain tube so turned the water off. Well that overflow/ vent just kept dumping water. It finally finished and i checked to see the gauge was now only showing 1/3 a tank of fresh water.

Wondering if anyone else has had this happen, how do you usually fill the tank?

Thanks

DSurette · 06-15-2015, 07:40 PM

If you stop filling before the overflow fills with water it will not siphon out. Once the overflow fills with water and starts siphoning there is no way to stop it without opening the overflow at the top of the tank. I installed a three way valve in the line on top of the tank to break the siphoning. This was on my first MH, a Coachmen Freelander 3150SS.

bowtie_guy · 06-15-2015, 09:02 PM

Ok so im not losing my mind that is what happened. I guess previously when filling since i didnt let it get that full it wasnt an issue. Will have to just pay better attention when filling.

Would have to drop that belly cover to do anything about it so ill pay better attention when filling.
thanks for the response!

retiredcamper47 · 06-15-2015, 11:38 PM

If you put some sort of "shutoff valve" on the end of the vent/overflow line to prevent the water surging out, make sure it is open when filling with water. If closed, your 40 something gallon water tank might become a 60 gallon real quick. It will also cause the 2 support straps to fail and drop down. Don't ask me how I know, I think I read a book on it once. Yeah, it was a book I read......

Bob

SKnight · 06-16-2015, 12:15 AM

Yeah, great design, isn't it?

I lengthened my vent hose and draped it over the LP tank. I installed a T valve at the bottom of the vent hose so that I can break the siphon loop and to let me know when it's full. I attach the hose, open the T valve, let it fill until it's running out the T. Then I close it, let it fill until it's pushing up towards the top. If I open the T, it will start pouring quite a bit of water on the ground. What I do is I use the fresh, then once it's down a bit I'll open the T and let it breathe normally.

Taranwanderer · 06-16-2015, 07:53 AM

This is my answer from another post, redacted, where someone was asking about identifying their vent tube. It's worth repeating:

The only other thing I'll add here is this: as you observed, it (the vent tube) doesn't have a valve, it's just an open hose that overflow drains the FW tank when it gets too full and allows air into the tank as you use water (so you don't create a vacuum inside the tank and possibly collapse the tank in on itself.) But what I found (both with my previous camper and my current one) is that when I would fill up my FW tank at home and then head out on the "up and down, up and down" interstates around here--by the time I got to where I was camping, I would often have lost a third of the water in the tank out the vent (like, it said "full" when I left home and said "2/3" when I got where I was going.) So I added a valve on the vent/overflow hose as well to keep the water in. You just have to remember to open it when you get where you're going (to allow air back into the tank as you use your water.)
__________________

WolfWhistle · 06-16-2015, 10:18 AM

Can't remember your model, B... but if like my 29hfs you don't have to worry straps breaking .. Tanks sit on angle iron side to side and welded to the frame... They are exactly correct otherwise... what happens when over filling... the overflow can't handle the volume... the tank pressurizes some.. then the overflow keeps flowing; turns into a siphoning action. Opening the drain until the overflow stops. You will have to add more water to top it off. naturally

retiredcamper47 · 06-16-2015, 10:47 AM

My 2 bottom straps were welded to the rear angle iron going frame to frame. The straps just laid across the front angle iron (not welded). The tank, while expanding, bent and pushed the front of the straps off the front angle iron. I made angle iron extensions for the two straps and bolted them to a support with carriage bolts. The tank had tilted and dropped below the front angle iron support. Had to use a hydraulic floor jack and a 2x4 to lift it back up into the angle iron support.

Bob

tjay · 06-16-2015, 09:35 PM

okay, so i used my fresh water tank on my new 2016 Vibe268rks for the first time this past weekend. I filled it til water was coming from overflow line. Gauge showed tank was full. By next morning tank was empty! I thought i had a leak in tank! when i hooked up trailer and it wasnt level, water poured out from underbelly! Could it have been this siphoning problem?? If so how do i fill tank without it happening again? Or should i bring it in to be looked at? sorry if these ???s sound foolish, i never had this problem with my '06 Cherokee.

tjay

2015 gmc sierra 1500
2016 vibe268rks

WolfWhistle · 06-17-2015, 07:09 AM

Tjay, the siphoning actions we are talking about is where water continues to flow from the overflow pipe. Is it possible when you topped it off you didn't notice water came out and continued to come out of the overflow pipe? I would think that if you have water inside the belly (above the belly cover) it sounds to me, you have a leak at the bottom of the tank; possibly the drain pipe is leaking at the bottom of the tank... loose or no teflon tape?? There isn't a foolish or dumb question here, my friend. We are all learning as we go. I would try filling it up again and try to see where it is coming from.

bowtie_guy · 06-18-2015, 04:08 PM

Well filled the trailer paying attention to the indicator. Seems to be ok so far. Tomorrow will be towing it and will check once at the camping spot.

DennisTD · 06-19-2015, 08:21 AM

I would think the overflow hose would be connected to the top of the tank. If that is the case I don't see how it could siphon. That can only happen if the overflow is running down into the tank. I wonder if Bullet Bob has some insight as to how the overflow is connected.

SKnight · 06-19-2015, 08:38 AM

Quote:

Originally Posted by DennisTD

I would think the overflow hose would be connected to the top of the tank. If that is the case I don't see how it could siphon. That can only happen if the overflow is running down into the tank. I wonder if Bullet Bob has some insight as to how the overflow is connected.

I can tell you exactly how it's attached in my Sierra. It's drilled into the side of the fresh tank with the bottom of the fitting about 1.5" below the top of the tank with the fill right next to it. You fill the tank, the fill pushes water to the backside of the tank, then once water comes out the over flow you turn it off. The water pushed to the back of the tank levels out and now you have water flowing out for ten minutes, usually below the full sensor.

And every time you turn, water will flow out.

And every time the trailer leans a little, even more will flow out.

So it doesn't really siphon in the true sense, but it looks that way.

I fixed mine with a T valve and a loop of hose draped over my LP tank. Now I can fully fill the tank and I won't lose any during travel.

DennisTD · 06-19-2015, 09:10 AM

Thanks for the information. I'll have to look at that on mine.

CAT-RN · 06-19-2015, 10:11 AM

I just pulled my vent hose up so that the end of it is above the tank. Wire tied it there. Drilled a couple more 3/8 holes in the floor just in case I over fill. All well. Hasn't overflowed since.

Russell

DSurette · 06-19-2015, 10:12 AM

On my Freelander 3650SS the overflow lines, there were two of them, went into the top of the tank and extended down into the tank. I don't remember how far down they went but once they started syphoning they drained out quite a bit of water. I eventually installed three way valves in the lines so I could break the vacuum once it started.

**Tireman9** · 07-01-2015, 08:48 PM

This almost sounds intentional. Can't believe a company that's been making RVs for 5 decades doesn't know how to vent a holding tank without creating a situation that allows a large % of the water to flow out

Will check this out when I take delivery of new unit in couple weeks. If water drains out I would consider this a design defect that needs fixing at company expense. That might get their attention.

WIll post what I discover in a few weeks.

I know Coachmen knows how to design a holding tank with proper venting. Our 2130QB had zero problems in 7 years and 25,000 miles with many tank fills to 100%.

bowtie_guy · 07-01-2015, 09:20 PM

Well on my most recent outting I left with the gauge showing full. Was able to see some water sloshing out during some slow going corners when stopping to get a coffee before hitting the road. 2 hour trip setup the trailer and found the gauge now showing 2/3rds of a tank.

WolfWhistle · 07-02-2015, 06:19 PM

Quote:

Originally Posted by bowtie_guy

Well on my most recent outting I left with the gauge showing full. Was able to see some water sloshing out during some slow going corners when stopping to get a coffee before hitting the road. 2 hour trip setup the trailer and found the gauge now showing 2/3rds of a tank.

You don't suppose the top light sensor is just not working? and you really have more? If you actually lost 1/3, how much water would that be?

bowtie_guy · 07-03-2015, 08:47 PM

Quote:

Originally Posted by WolfWhistle

You don't suppose the top light sensor is just not working? and you really have more? If you actually lost 1/3, how much water would that be?

I tend to think it's right about losing water. What I did was filled the tank, when the full light came on I went and turned the water off so it wasn't full to the top but into the full range. Some water spilled out along the way to the point once setup it was showing 2/3rds.

18 gallons would be a 1/3rd of a tank.

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