what about a check valve on the tank overflow tubes?

[pconroy]

A couple of times, we've filled the fresh water tank then drove a bit to the next stop only to find the tank 2/3rds or so full.

I'm wondering if the overflow tubes start to siphon and drain the tank. They're not easy to access so I don't think I want a valve.

But what about a check valve? A one-way check valve?
That should work, wouldn't it?

[Hivoltage98]

Possibly. But the tank needs to be able to breathe otherwise it would become air locked.
Following. [emoji1]

[oldmanAZ]

I'm not sure what kind of one-way/check valve you have in mind. Those vent tubes are meant for air to pass in both directions.

For a permanent, one-time fix, consider extending the tube and routing it up above the tank and pointing back down. That should prevent the siphoning without valves, plugs, etc.

[in the wind]

Originally Posted by oldmanAZ

I'm not sure what kind of one-way/check valve you have in mind. Those vent tubes are meant for air to pass in both directions.

For a permanent, one-time fix, consider extending the tube and routing it up above the tank and pointing back down. That should prevent the siphoning without valves, plugs, etc.

Good suggestion.
How many tubes are there and what do they look like?

[pconroy]

There are three on mine. They're the white 1/2" ID water hose just like the rest of the plumbing.

[RVhiker]

A lot of folks have the problem of water siphoning out the overflow lines. Many have installed simple valves at the ends of the overflow lines. I used two 1/2" PEX ball valves.

The valves must be open when the tanks are being filled, otherwise the tanks can rupture; or the pump can collapse the tanks when suctioning water out of the tanks.

Here's what I do. When filling the tanks, at the first trickle of water out the overflow lines I shut off the flow of water into the tanks and close the valves. Usually a day or so of water use is necessary before the valves can be opened; the water level in the tanks must drop enough so that water does not continuously run out of the overflow lines.

pconroy, with three overflow lines do you have three fresh water tanks? Maybe one of the lines you are seeing is a low point drain for your piping?

[SloPoke]

Our Seneca has three vent tubes, all routed from the top of the tank-along the wall and thru the wall to the outside of the compartment. I put the shut off valves as RVHiker did as there is not enough room above the tank to route the vent lines to avoid the siphoning.

RobbyR put together a home made vacuum breaker on his... Search for his post on the project.

[Robbbyr]

Originally Posted by SloPoke

Our Seneca has three vent tubes, all routed from the top of the tank-along the wall and thru the wall to the outside of the compartment. I put the shut off valves as RVHiker did as there is not enough room above the tank to route the vent lines to avoid the siphoning.

RobbyR put together a home made vacuum breaker on his... Search for his post on the project.

https://www.jaycoowners.com/forums/f...ank-54228.html

This is a link to the post talking about the vacuum breaker, it is described in post #8. I put it together from PVC fittings, it provides a separation between the connections to the tank and to the overflow/vent lines. It also is where I plumbed my hot water recirculation return line, that is the red pipe in my picture. That red line not needed if one just was looking to create a vacuum break.

[GeorgiaRV]

I put a plastic on/off valve in each of the three overflow tubes. I open them when filling the tank until water flows out. then shut them when traveling. re-open one or all of them depending on how level I am when I arrive at camp site. This has worked flawlessly now for almost 6 months.

[pconroy]

Thank you all for the correction and suggestions!

[201822j]

Like many here this is common. My new RV experience:
While filling tank for the first time I thought what happens when the tank gets filled, then all of a sudden water started pouring out the bottom of the RV. There I saw 3 white hoses draining water. Ah there is the overflow. Drove to camp ground a few hours later, checked fresh water level WHAT 1/4 filled.
I was bitten by the Siphon effect.
The problem with my Redhawk is the tank is mounted up against the floor. I'm guessing many RVs are this way so you can't route the hoses above the tank. Check valves won't allow the hose to operate correctly. The only solution I can see is to extend the hose out to the edge and add manual valves that can be closed while driving.
Or drill holes into the floor and loop hoses up above tank level (I'm not doing that)

[Wertles]

I took the cheap, easy way out. I placed a AA battery in each tube after fill up and took one out when I reached my destination. I had plans on adding valves but never found time to do that so the battery trick worked for over a year.

[Crossingover]

Originally Posted by Wertles

I placed a AA battery in each tube after fill up and took one out when I reached my destination.

That's an awesome fix! I was about to ask the other poster what size valves he used but now I'm going your route with the AA batteries. Thanks for sharing.

[norty1]

most are 1/2 inch pex.

[MD3]

I had found a 1/2" push on fitting for a dip irrigation system that has a screw on cap on the other end. Problem wasn't capping/blocking the vent hoses it was having to crawl underneath after filling it to cap it... then crawling back underneath to uncap it when we get to where we are going. My tank vents are almost directly underneath the middle of the RV.

I had three of these push on caps on mine but going to pull them off.
Worked great but don't like crawling in the dirt.

I'm going to do an airgap setup like Rusty or Rob and then be done with it.

Home Depot has the caps for $1.54
https://www.homedepot.com/p/DIG-1-2-...-Q58/100125237


_

[CaptRon53]

I took the really easy route and folded the ends overflow hoses over and zip tied them in place. The fill cap on our fresh water tank is not air tight so air can flow in and out of the tank as needed to equalize the tank. I have had no problems with this solution with multiple boondocking trips over the last 1 1/2 yrs.

[Robbbyr]

Originally Posted by CaptRon53

I took the really easy route and folded the ends overflow hoses over and zip tied them in place. The fill cap on our fresh water tank is not air tight so air can flow in and out of the tank as needed to equalize the tank. I have had no problems with this solution with multiple boondocking trips over the last 1 1/2 yrs.

Works if you have a gravity fill port, many of us do not. Wish I did however!

[oldmanAZ]

Originally Posted by CaptRon53

I took the really easy route and folded the ends overflow hoses over and zip tied them in place. The fill cap on our fresh water tank is not air tight so air can flow in and out of the tank as needed to equalize the tank. I have had no problems with this solution with multiple boondocking trips over the last 1 1/2 yrs.

IMO, the venting is not needed when getting water out of the tank(s). The vents are there let air escape when filling the tank with water. Depending upon how the tank is filled, if there is not sufficient capacity for air to escape then the system can become pressurized enough to damage the tank.


EDIT: Oops! See Robbbyr's post. My post may not be true for ALL RVs. Sorrry.

[Robbbyr]

Originally Posted by oldmanAZ

IMO, the venting is not needed when getting water out of the tank(s). The vents are there let air escape when filling the tank with water. Depending upon how the tank is filled, if there is not sufficient capacity for air to escape then the system can become pressurized enough to damage the tank.

I respectfully disagree about some of us needing air vents being open to use the water. A fellow Seneca owner experienced a collapsed tank due to restricted venting. For those of us with no gravity fill, you have to allow air back into the tank if you pump out (use) a significant amount of water. If you block the vents on a rig like mine you have a completely sealed system. My tank has only 4 openings. One is the fill/drain line entering the bottom of my tank. Then I have three vent/overflow ports on the top of the tank.

Attached post has pictures of the collapsed Seneca tank: https://www.jaycoowners.com/forums/f...ank-54228.html

[wducat]

I have this issue on my Seneca. On the Seneca, there are 3 overflow tubes right next to each other. Jayco has recommended that I add a 45 degree to one of them, and route a tube from that to the top of the compartment, letting the other two do the overflow work. The theory is that a siphon is being created, and routing one hose high will break the siphon. Have not tried it yet, but it is the official recommended fix I got from them when I inquired.