Community Forums

rcmedic · 05-16-2025, 11:13 AM

While I continue my efforts to upgrade my 20 year old Tropical T-396, I noted that my 100 gallon water tank has a large area in the center of it that has become grossly concave and results in a a dramatic loss of capacity. It should have had some sort of internal support to prevent this very issue but it does not. My question is: has anyone else come across this? How did you address it? The challenge come in that I can fill the tank and force the tank to expand back to it original size/form but because the tank has developed a memory for the concave position, it squeezes the water back out through the Overflow/vent line. Since the tank is otherwise in good condition, I would rather not have to purchase a new one. Any help/advice would be much appreciated.

Flyer15015 · 05-16-2025, 11:22 AM

Nedic.
100 gallons is a LOT of water to be hauling around. 834# per Google.
I would say it's better for the tank to be bowed in than out.
Are you confident there is enough support under the tank?

Just asking....

Mike in Colorado

rcmedic · 05-16-2025, 11:39 AM

Quote:

Originally Posted by Flyer15015

Nedic.
100 gallons is a LOT of water to be hauling around. 834# per Google.
I would say it's better for the tank to be bowed in than out.
Are you confident there is enough support under the tank?

Just asking....

Mike in Colorado

Yes, It is the original tank to the unit. Been holding for 20 years.

DustyDriver · 05-16-2025, 11:44 AM

The concavity may have resulted from draining the tank without properly venting it during the process, which can cause the tank to collapse or, worse, crack. Since filling it with water does not seem to pop it back into shape, it looks like you may have to settle for limiting how much you pump into it from now on. A new, adjusted “full capacity”, if you will.

DD

bentjm · 05-16-2025, 02:42 PM

How much is "grossly"?

1, 3, 10, ... inches? Depending on the dimensions of the tank, it may only be a few gallons.

US1 · 05-16-2025, 03:48 PM

Quote:

Originally Posted by bentjm

How much is "grossly"?

1, 3, 10, ... inches? Depending on the dimensions of the tank, it may only be a few gallons.

I agree. It won’t make but a couple gallons at most loss. The sides and the corners would have to colapse also to make a noticeable loss.
I’d double check the vent hose to make sure it’s open.

ViperJD · 05-16-2025, 04:41 PM

Some of the comments seem off. We REGULARLY travel with full water in our tank, so this could be a big deal. When we boondock in places like Quartzite and elsewhere, every gallon matters. I agree that a concave top may only reduce 1-10 gallons, but it might matter. Short of going in through the side of the RV (top would be better, but flooring is a bear), there are not many ways to fix the tank.

RCMedic, I would give it a shot by trying to get at it from the side, and installing a hook or loop on top (glue to top, not via a hole) and see if you can pull it back up. If not, you may be stuck with what you have, or be forced to replace. My 100 gallon tank actually holds about 110 gallons (measured via meter on input), so we don't come off of full for the first few showers while boondocking.

All the best,

Av8ter150 · 05-16-2025, 04:57 PM

Quote:

Originally Posted by Flyer15015

Nedic.
100 gallons is a LOT of water to be hauling around. 834# per Google.
I would say it's better for the tank to be bowed in than out.
Are you confident there is enough support under the tank?

Just asking....

Mike in Colorado

Traveling with full water will depend a lot on the coach. I don't know what his cargo carrying capacity is but on my Monaco road ready with full fuel (130 gallons) and a full 100 gallons of water I still have 7000 pounds until I reach gross weight. So, he may not have any issues hitting the road with a full tank.

SafariBen · 05-16-2025, 05:07 PM

Since you mention it, I'd try filling the tank by blocking the overflow, then heating the the water, or the top and leaving it for a while in storage. It will take a LONG time to heat up that much water, a heat gun on the top may be the easiest method, with NO water in it. Air pressure may be one method, but riskier than water. You'd want to watch the tank while heated so it doesn't over expand.

Unplanned Tourist · 05-16-2025, 05:25 PM

If it's not too hard to take out, why not pull it and expand it with air pressure (VERY carefully) on a hot sunny day. Put someting like a sheet of plywood on top and let it sit until it cools down the next morning. Nothing to loose but some time. If it doesn't work out, just replace it.

Gary RVRoamer · 05-16-2025, 06:48 PM

If you can apply moderate heat in some manner, you can probably retrain it to its former capacity.

Ray,IN · 05-17-2025, 03:39 AM

My water tank tops (2 50G tanks) also sag in the center; gravity at work. The only solution is to add a prop/support in the center of the tank.
I'd be very careful about trying to pressurize the water tank to correct the deformity. These tanks are not designed to withstand internal pressure. If you break one, then you have a much larger problem.

Country Road · 05-17-2025, 05:15 AM

I’d probably leave it as is but I would find out exactly how much volume was lost. Then, on the rare occasions when you need max capacity water, I’d carry a collapsible bladder tank with a pump to get the water transferred.

Domo · 05-17-2025, 08:21 AM

20 year old plastic.

I would hold out very little hope the old plastic/nylon/manmade material is capable of being effectively repaired.

If me, I'd measure the capacity by determining the flow rate from my hose (how many 5 gallon buckets can be filled in how long). Then I'd fill the tank and time it to estimate the total water it takes - without overfilling to the point it's burping.

We'd be interested to learn how many gallons it really holds with the concavity.