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Fresh Water Mysteriously Missing from RV Water Tank

Fresh Water Mysteriously Missing from RV Water Tank


By avatar  Scott
Posted On 07/05/2018 18:42:08
Trip Date 04/07/2018  

Camping | water missing | water leaking | water tank | fix water overflow | overflow tube leaks | overflow tube drains water | overflow tube | customizations



On several recent occasions while on a long trip with our RV, I noticed that the water in the RV fresh water tank measured empty on the control panel - even when it had just recently been filled. The tank actually was empty, and no water would pump. I started paying closer attention to the water I put in the tank and the fresh water tank sensor readings - which I knew were unreliable.

Observations on Water in my Tank

I filled the tank one day before traveling and the sensor said full. Only about 3 hours later when I got to our park, the sensor said empty. The water didn't last long and the tank ran dry. Hmm. Where is this water going?

I starting doing online research and found that many others had this problem too. There are many theories about how the water gets out of the tank. In my case there wasn't a leak, there didn't seem to be water inside the RV or on the ground (on a level area). One theory was that the wind creates a Venturi effect on the end of the overflow hose, sucking water out of the tank. Another theory was that the movement of the vehicle creates a pumping effect and pumps the entire tank dry. I was skeptical of any of these explanations, and many others.

On my next drive, I filled the tank again. Usually I only fill about 1/2 or 3/4 of a tank, but I filled it full this time. On my drive, which was through some hilly country, I needed to stop at a gas station for a restroom break. I pulled into the parking area and parked along the side since I wasn't getting gas. I got out and thought to look at the overflow tube. Wow - it was flowing water out onto the parking lot. The RV was parked on a sideways slope with the driver's side down.

So now I knew that the water was coming out of the overflow tube (a white tube dropping straight out of the bottom of the RV) and onto the ground. Surely it wouldn't empty the whole tank - or even most of it, but there was a significant amount of water flowing. I had been driving back and forth on hills and, most importantly, tight turns which had sideways banked roads. I don't know how much water came out during the drive. I experimented with the city water / tank fill valve to see if it would stop the water from flowing, but it seemed to have no effect.

This is crazy. RVs have been around for a long time and the manufacturers haven't fixed this problem? Maybe it doesn't happen on all models - I have a Highland Ridge Open Range 2910RL, which I do really like.


Finding a Good Solution

I did more research looking for how others have solved this problem. Most solved it by capping the tube, putting a valve on the end or even a rubber band around a zip-lock bag on the end of the tube. Many online commenters are concerned that if you fill a tank that has a cap or valve on the overflow, it can't overflow and the hose pressure will balloon the tank and burst connections inside the RV. This would cause an interior flood which is not good. Also, many don't want to climb under the RV to mess with this. My overflow tube is way under the RV and behind the wheels. When the slide is out, it is very hard to reach without getting dirty or muddy.

I was about to travel to some places in Missouri where the state parks don't have water at the sites and where I knew the other water service was turned off due to freezing weather in the forecast. It wasn't quite boondocking, but there was no water. I would need to arrive with a full tank. I wanted a fix so I could get water before arriving at the park.

My Solution To Stop the Overflow Tube Leak

I decided to put an elbow joint and run a tube to the rear of the RV with a valve so that I could easily open it when I'm filling the tank, and keep it closed otherwise.


Elbow and Extended Drain Tube

Elbow and Extended Drain Tube

After obtaining my parts at the local Lowe's, I cut the tube to the right length and push connected all the Shark Bite parts. I then used zip-ties to connect it all to the RV.


Parts that I Used

Parts that I Used


Cutting Tube to the Right Length

Cutting Tube to the Right Length


Push Connect All Pieces

Push Connect All Pieces

The result is easy to reach and to operate. Normally my RV is in city water mode so I keep this valve closed. Only when filling the tank do I need to open this overflow valve. After filling, I can close it again to keep all the water inside.


Easy Reach Valve at the Rear of the RV

Easy Reach Valve at the Rear of the RV

My theory is that this problem is based on the geometry of the fresh water tank. The tank is flat and wide so it is not very deep. The overflow tube and fill tube are at the top, and the pump tube and drain tube are at the bottom. My RV has an insulated bottom so I can't see it - but I did research what they look like. I also read that the overflow tube might have a little extra tubing on the inside of the tank that hangs down, meaning that the tube is not actually at the top of the tank.

Imagine the tank with a healthy amount of water sitting on a slope leaning such that the overflow tube is on the downhill side. The water level, instead of being at the top of the tank, might be way up toward the uphill corners at an angle. The overflow tube, instead of being near the top of the tank, might be half way through the depth of the water. This allows water to flow out (especially if the fill tube is on the opposite side and can act like a vent).

How much can come out? Well, if the tank is 12 inches tall but on a slope (where the far end is up 12 inches), the overflow tube might be at a point halfway through the water depth. If there is 2 additional inches of tube dangling inside (speculating), you could possibly lose another 2 inches of water. When the tank is at an angle and there is enough water pressure, water starts flowing into the overflow tube. The flowing water starts a siphoning action which can continue to suck water. This could be 3/4 of your tank or more, and is not good if you need the water!


Fresh Water Tank Geometry

Fresh Water Tank Geometry

Anyway, with my fix, it works much better. I just need to remember to open the overflow drain valve when I fill the tank.


I admit that the actual scientific reason for the loss of water is a bit of a mystery, but I now know that it comes out of the overflow, and this fix will stop that.

Finding the Plumbing Parts

Reminder: This Wordy Explorers post contains affiliate links. If you make a purchase through this link, we will earn a commission at no extra cost to you. Thanks for reading!

You can easily find these on Amazon and get home delivery (remember to verify your overflow tube size):




Fresh Water Mysteriously Missing from RV Water Tank



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Created On 05/02/2018 15:37:49  
Updated On 08/23/2018 16:43:20
Scheduled On 06/30/2018 20:42:08
Posted On 07/05/2018 18:42:08
Last Editor Stacy
Location  Red Bluff Campground, Missouri
LinkId  WaterMissingFromTank
StoryId  1525289869765





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