Now....most overflow fittings I've ever seen are mounted towards the top of the tank. Just a threaded 90 degree, usually barbed on the end. There is no tube on the inside of the tank connected to that fitting. Now if anyone knows how siphoning works...you would have to have a tube going all the way inside the tank to create the effect. Once the water is below the overflow fitting...DONE ! air prevents anymore from being sucked out. Now while you're driving...yes you're going to get some "Splashing" of water out the overflow, but to splash 3/4 of a tank out that fitting....I'm having my doubts.
Now....most overflow fittings I've ever seen are mounted towards the top of the tank. Just a threaded 90 degree, usually barbed on the end. There is no tube on the inside of the tank connected to that fitting. Now if anyone knows how siphoning works...you would have to have a tube going all the way inside the tank to create the effect. Once the water is below the overflow fitting...DONE ! air prevents anymore from being sucked out. Now while you're driving...yes you're going to get some "Splashing" of water out the overflow, but to splash 3/4 of a tank out that fitting....I'm having my doubts.
Many of these tanks have the vent attached somewhat below the top of the tank on the side. It SHOULD be on the TOP of the tank, but it's not. So it's very easy to siphon out a fairly large volume of water from the tank on a long drive. There are tons of postings on this issue on the forum.
The vent line really should be run up a wall somewhere and have a small U-bend that ends above the tank. But that's difficult to do given the location of most FW tanks.
My Salem fwt drains when driving also. My last trip I put a bolt in the overflow and it didn't drain. I'm going to reroute the overflow tube before my next trip.
Thanks for all of the recommendations!! Until I get a valve installed, I am placing a simply party balloon (20 for $1) on the end of the hose while driving. The balloon neck is tight enough to hold water in the line while driving (from sloshing), but has enough give so that it is pushed off if I forget to remove it when filling. And prevents syphoning while driving. I'll attach photos once I get a permanent fix.
Siphoning appears to be the consensus view.
But, when assembling my camper, a worker drove a screw through the floor right above my fill hose/pipe. It penetrated the hose, and I would lose half of my water.
Verify that you have NO detectable leaks under the camper to rule out a similar problem.
I had to cut the fill hose at the leak, use a Dremel tool with a cutoff wheel to trim the screw, then use 1 1/4" plastic pipe from a (new) bathroom J-trap and hose clamps to mend the hose. No more leaks.
If it is siphoning, a simple solution would be Gorilla tape over the end of the exposed vent hose next to the fill pipe. This will disrupt the aerodynamic flow over the end of the vent. It's that small vacuum over the exposed vent that creates suction that starts the siphoning. If there is a vacuum, it may attract dirt to the vent, and as unlikely as it may be, that dirty might contaminate your water, especially if it's in road spray.
If the tape works, you might add a more permanent solution in the form of a hinged, flip up cover that protects the area from contamination and changes the aerodynamics in the vicinity of the fill and vent pipes.
__________________
Jim & Renee
2020 Jayco Jay Feather X-213
previously 2014 Forest River/Rockwood HW 277
2006 Ram 1500 4WD Crew with Firestone Airbags
Every weekend boondocking in the National Forests or at Lake Vallecito.
My old travel trailer would spew water from the fill when driving through areas with heavy side gusts or when passed by a semi.
Trailer would tilt one way, water followed it. Trailer tilted back and water would do likewise only keep running right up the fill hose and out the side.
I hated the water tank in that trailer to the point I refused to dry camp anymore. Didn't want to haul ANY water in the tank.
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"A wise man can change his mind. A fool never will." (Japanese Proverb)
"You only grow old when you run out of new things to do"
2018 Flagstaff Micro Lite 25BDS
2023 f-150 SCREW XLT 3.5 Ecoboost (The result of a $68,000 oil change)
If you fill your fresh water tank while connected to your rig, and your camper is in a slight nose low attitude, your tank will overflow at about 1/2 full. The reason is in most trailer installations, the overflow/fill tube is in the front of the fresh water tank and the level indicators are in the rear. (see photo)
Also there is usually a "U" in the overflow tubing where water can lay. While driving down the road, a Venturi (suction) is created at the tube outlet. Once the water in the tube starts to vent overboard, it can actually suck water out as you drive.
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Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
If you fill your fresh water tank while connected to your rig, and your camper is in a slight nose low attitude, your tank will overflow at about 1/2 full. The reason is in most trailer installations, the overflow/fill tube is in the front of the fresh water tank and the level indicators are in the rear. (see photo)
Also there is usually a "U" in the overflow tubing where water can lay. While driving down the road, a Venturi (suction) is created at the tube outlet. Once the water in the tube starts to vent overboard, it can actually suck water out as you drive.
Do you think adjusting the hitch height to have the camper level while hitched would reduce this phenomenon? My PUP is slightly tongue-high while being towed due to my choice of hitch drop, slight increase in air pressure in the rear tires, and about 30 psi of pressure in my airbags. This arrangement eliminate any porpoising going through whoop-dee-doos in pavement and dirt roads. Since I fixed the leak (screw penetration), I always arrive with a full water tank regardless of how far I drive. But the aerodynamics around my fill pipe may not foster siphoning. Could just be dumb luck. What do you think?
__________________
Jim & Renee
2020 Jayco Jay Feather X-213
previously 2014 Forest River/Rockwood HW 277
2006 Ram 1500 4WD Crew with Firestone Airbags
Every weekend boondocking in the National Forests or at Lake Vallecito.
Siphoning appears to be the consensus view.
But, when assembling my camper, a worker drove a screw through the floor right above my fill hose/pipe. It penetrated the hose, and I would lose half of my water.
Verify that you have NO detectable leaks under the camper to rule out a similar problem.
I had to cut the fill hose at the leak, use a Dremel tool with a cutoff wheel to trim the screw, then use 1 1/4" plastic pipe from a (new) bathroom J-trap and hose clamps to mend the hose. No more leaks.
If it is siphoning, a simple solution would be Gorilla tape over the end of the exposed vent hose next to the fill pipe. This will disrupt the aerodynamic flow over the end of the vent. It's that small vacuum over the exposed vent that creates suction that starts the siphoning. If there is a vacuum, it may attract dirt to the vent, and as unlikely as it may be, that dirty might contaminate your water, especially if it's in road spray.
If the tape works, you might add a more permanent solution in the form of a hinged, flip up cover that protects the area from contamination and changes the aerodynamics in the vicinity of the fill and vent pipes.
I'm pretty sure that the rigs that have a vent line as part of the fill connection do NOT have a siphon problem. The vent line on these typically is routed with the fill line, and the fill line does not go up and then down into the tank. The folks with siphon problems are the folks with the vent line hanging down under the rig.
For example: I have a gravity fill with a vent next to it. The gravity fill clearly has no inverted U in it (or it would never fill). The vent line is run with the fill line, so it has no inverted U in it. So both lines run UP from the tank to the fill connection. So no siphoning.
Your experience may differ. It is totally based on tank orientation and levelness when filling and using.
If you have a tank like mine and raise the nose of the camper to get it 100% full, then lower the nose to hook up again, the water will just run out.
Understanding how your tank is oriented will help you get the maximum amount of usable water.
If your lower connection (that goes to the water pump) is tilted up, you will have a conciderable amount of unusable water in the tank. Tilted down, you can use it all.
So tilt your camper one way to get as much water as you can into it; then tilt it the other way to get the most out.
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Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
Ok. Problem solved. I simply put a party balloon on the over-flow while driving.
The balloon has some water in it when I arrive at next site. But water tank is still above 66%.
I remove the balloon before starting the water pump at next site.
We are dry-camping 5 days per week.
Attached is a photo with my fix. I’ve add two 1/4-turn ball valve.
After filling to Fresh tank to 100%, I close one valve and place a balloon on the open valve to prevent tank rupture in the event of elevation changes or temperature changes (the balloon will fail, before the tank ruptures).
It works flawlessly. When I arrive at the boondocking spot, I simply remove the ballooon OR open the 2nd valve to prevent a vacuum inside tank when I start using the water pump.
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