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Big Boom in our RV Fresh Water Tank! (and What We Did)

Big Boom in our RV Fresh Water Tank! (and What We Did)

avatar   Scott
Trip Date 11/15/2018
Posted On 02/23/2019 15:55:58

Camping | Hacks | RV | RV Water Tank Repair | RV Fresh Water Tank | Filling RV Water Tank | Overfilling RV Water Tank | RV Water Pressure

Just after setting up our RV in Mesa Verde National Park, we heard a loud pop. What was that? It definitely sounded like the pop came from underneath the RV. Since we were inside relaxing, we ran outside see what what going on. I quickly realized that when I turned on the water, the water input selector was on "tank fill" and not "city water" mode. I was accidentally filling the tank when I thought I was just connected to city water. I immediately flipped the selector valve, but what caused the loud pop? It didn't happen immediately, but soon there was lots of water flowing out the sealed bottom of the RV. Oh man!

Although we hope you are never faced with a similar situation, take a look below to read about the diagnosis and repair. Fortunately I was able to repair our fresh water tank with minimal cost other than time ... but had lots of questions and frustration along the way that maybe you can avoid.

Big Leak From Under the RV

Because our RV has a sealed polar bottom, I couldn't easily see what the issue was. Since the water input selector was in tank fill mode and I had turned on the water with a healthy amount of water pressure, I realized that I either broke a fitting or the water tank itself busted. Although I did have a water pressure regulator on, somehow the pressure and water flow was just too much. The tank filled up and since I was inside and not watching, it soon overfilled and eventually something popped. Unfortunately since it was near dark, we were on the road, and it was cold, I wasn't about to try any serious attempt to diagnose the issue as it was going to require taking the RV apart.

I was able to determine that there were no leaks above the floor line inside of the RV. I also noticed that the water that was flowing out onto the ground was at a point that was about 10-15 feet forward from where the water tank and hoses are located. After the dripping finally stopped, I experimented with the water input selector and water pump to try to determine where the leak was. I concluded that it was either the fresh water tank or the hose that connects the tank and the water pump.

I was hugely upset and frustrated with my mistake!

Short Term Solution

With about 4 weeks remaining on our scheduled trip, I was pretty sure that I would not have time to figure out the location of the leak and fix it while still on the road. The good news was that I was able determine that the city water mode would still work - it was just pumping water from the tank that didn't work as the leaking only occurred while filling the tank.

The bottom of the polar thermal package on our RV was one solid piece of corrugated plastic that was nailed to the metal frame of the RV. The bottom of the RV wasn't flat, but it was bowed down and, from what I could tell, was filled with water. To make things even worse, we were traveling in near freezing temperatures!

I found the low spot in the bottom cover and carefully poked a hole through it at a point where I was sure it wouldn't go through any of our other tanks (grey or blank). This finally allowed the water to fully drain out.

While still on site, I popped out a few of the nails from the side of the RV bottom. The nails were holding the plastic up and I wanted to try see underneath. I couldn't see much, but I was able to localize where the leak came from. It was definitely near the fresh water tank, which was no surprise to me by this time.

Nail and Washer Holding up Underliner

Nail and Washer Holding up Underliner

The Diagnosis

Weeks later when we got home, it was time to figure out what the issue was. I didn't want to take it to an RV dealership for repair because it would likely cost much more than I wanted to spend. So, I decided to try to diagnose and fix it myself.

I studied the bottom carefully to determine where and how to open the bottom. (I wanted to avoid removing the entire bottom piece because it was 33 feet long plus there are other wires and hoses that pass through the sealed plastic around the wheels.) I finally decided to make a cut from side-to-side through the solid plastic bottom at a point (specific to my situation) between the wheels and the rear. I certainly did not want to use a knife of any sort to make this cut, so I used short rounded end scissors to avoid damaging anything.

I knew that I wanted to replace the nails with screws in order to securely hold the bottom, so my next step was to remove the nails. I had read that a crowbar would work, but since I didn't have one I used a long screw driver and a claw hammer. Using the screw driver, I pried each washer high enough to get the claw in. This worked fine as long as I could get a good angle on the nail. It was definitely a challenge near the wheels due to the suspension mechanism. Once all of the nails between the cut and the wheels were removed, I had a large flap that I could fold down.

Still Mounted Water Tank

Still Mounted Water Tank

By this time, the bottom was dry so I began slowly filling the RV water tank. While it was filling, I crawled underneath with some dry paper towels to try to locate where the water was coming from. I finally concluded that the water was leaking from the center of the tank.

In our case, the water tank geometry is like this:

  • The tank is about 6 feet wide and 4 feet from front to back.
  • The tank is about 8 inches high and is suspended in a metal frame attached to the trailer frame.
  • The bottom of the tank is domed, however in the center there is a 3 inch diameter donut hole that passes from the bottom to the top of the tank by design.
  • The tank is molded from two pieces and is made of a milky white plastic.
  • The bottom and top pieces are seamed both around the outside and around the inside of the donut hole.
Hmm, why is there a donut hole in the tank? Since the sides of the tank are somewhat flexible, I think the connection in the middle is to add stability to the tank and to help prevent the top from ballooning too much away from the bottom.

Donut Hole through Water Tank

Donut Hole through Water Tank

I also noticed that in the center (where the seam was), the top and bottom plastic pieces were not perfectly aligned. This created a thin weak area at the point where the two plastic pieces met and overlapped. Apparently, when I put too much water in the tank with too much pressure, the weak seam popped, and this is where water now comes from.

The Repair

I couldn't really see the point where the leak was very well, but I didn't want to remove the water tank from the RV because of the work and hassle involved. I could, however, reach the leaking seam with one hand at a time. (Since the donut hole was only about 3 or 4 inches in diameter, only one hand would fit into the space to feel where the leak was.)

I read that the tank was likely make out of LDPE (Low Density Polyethylene). I was originally thinking that I might use Flex-Seal to fix the tank or the hose. I read, however, that although Flex-Seal bonds to almost anything, is does not bond to LDPE very well. I then read that EternaBond tape (used for sealing the roof of an RV) can also be used on fresh water tanks and it does bond to LDPE.

EternaBond Tape

EternaBond Tape

I also read that J-B WaterWeld was a product specially formulated for plastic tanks and it worked well on LDPE. (I was familiar with J-B Weld for metal as I had used it before.) I even watched a You-Tube video about how someone else fixed a water tank (although his was not still mounted under the RV).

J-B WaterWeld

J-B WaterWeld

After discussing the issue with a friend, we agreed that I should use J-B WaterWeld and then cover it with EternaBond tape. (I wasn't sure if working with super-sticky tape was going to be very easy in such a confined space with only one hand.)

I bought a few packages of J-B WaterWeld and eventually returned to the store for more as I used 4 packages in all. As recommended by the instructions, I started by drying and sanding the edges. The J-B WaterWeld product is an epoxy with a Play-Doh like consistency. I used half-piece chunks and kneaded each until ready. I then flattened them until I had pieces that were thick enough but still large enough to cover the seams with an overlap of about 1 1/2 inches on both sides. I worked my way around the inside of the donut hole and covered the entire seam. The "Play-Doh" eventually bonds to the plastic and hardens into a strong patch. I think things went well.

After Applying J-B WaterWeld

After Applying J-B WaterWeld

After letting the patch cure for 24 hours, I tested it by filling the tank. My hope was that, after the tank was full of water, it would feel dry to the touch and after wiping it, my paper towels would remain dry. All seemed good!

I decided against covering the patch with EternaBond, because I don't think it would have added that much of a benefit - plus it would have been very difficult to work with in such a confined space. Since the J-B WaterWeld bond is supposed to be very strong, I was happy with the results.

My next step was to work on sealing the bottom of the RV back up. The nails with washers that I pulled out by claw hammer left holes (similar to pilot holes) in the metal frame of the trailer. I had read that, in order to replace the nails I should use self-tapping non-rusting screws so that they could be easily removed in the future. I found self-drilling #8 - 3/4 inch zinc hex-head screws at my local hardware store. I also purchased some new washers that were larger than the previous ones as the plastic was a little damaged from removing them.

When I tried to screw my newly purchased screws into the pilot holes, the heads just twisted off. Ugh - the pilot holes were too small. I ended up having to drill out the pilot holes making them one step larger so that the screws would fit without breaking.

Finally, I needed to seal the cuts in the plastic. I started by cleaning the plastic and I then used Gorilla Tape which bonded very well.

Winterizing Until Next Season

Since it was mid-November by this time, I needed to drain the water tank and winterize it. I then put the RV away for the season.

When I begin using the RV again, I will need to be much more careful. I always tried to follow this plan, but realized that I either got lax or just plain forgot:

  • Carefully check and recheck the water input selector setting.
  • Check the pressure of the water.
  • Stay outside and watch closely when the tank is filling.
I think my fix will continue to hold as long as it is not over-filled with water again!

Hopefully, my sharing of this experience will help you to avoid such a problem with your RV. But, if you do encounter a similar issue, maybe you'll be able to fix it yourself. The repair costs were minimal - just the cost of 4 units of J-B WaterWeld, Gorilla Tape and some screws to replace the ones that I removed. It was certainly much better than replacing my tank along with the associated labor costs that I would have had to pay to a service center.

RV Fresh Water Tanks

Want to learn more about your RV fresh water tank? Don't miss the related posts below for helpful information including how you can use an Aquatainer or what to consider if you notice that you have Fresh Water Mysteriously Missing from your RV Water Tank.

RV Water Tank Repairs

We'd love to hear about any experiences that you've had with repairing your RV water tank. Please share what prompted the need and a brief overview of how you made the repair, as well as any tips or suggestions. Just select the Add Comment button below.

Big Boom in our RV Fresh Water Tank! (and What We Did)


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JB waterweld fix
avatar   Jim Pergande

04/01/2020 11:26:50

Curious as to when you did your JB waterweld fix and how it has held up. I'm looking for a similar solution. Thanks.
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Water Tank Repair
avatar   Scott
04/01/2020 13:30:27

Hi Jim - Thanks for the question. I did the repair in 11/2018. We used the RV for several long (6+ week) & short (days to 1 week) trips during 2019 with no issues. I winterized the RV in 12/2019 & before leaving in 1/2020 for a 6+ week trip, I was not as careful when refilling the tank (used higher water pressure). I noticed a small leak which I haven't investigated - it's possible that the patch may have a minor leak. Before we leave again, I'll figure it out!

Hope that helps, Scott
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