Fresh water tank emptying 20%

Miwok · October 2025

2015 CSS: Our freshwater tank only empties 20%. The tank is clearly 80% full. The pump has been confirmed as working fine. As the valve is at the front of the tank (design flaw?), has anyone tried installing a valve at the rear?

A group of competent RV problem solvers concurred with the above analysis. This problem must have been addressed by someone previously.

Sharon_is_SAM · October 2025

Is the valve blocked? Try blowing air into the valve and see if there is debris settling in the valve.

Miwok · October 2025

Tried. Problem persists. We fill up the tank and get the same 2 gallons only out.

Sharon_is_SAM · October 2025

Even with the tongue fully down?

Miwok · October 2025

we tried that as well without notable success. It would not have been a sustainable solution, for tipping the tongue down when we need water would not make sense.

rfuss928 · October 2025

Is it possible the fresh water vent tube is blocked? After a couple gallons are used the tank becomes air locked...

jbajor · October 2025

When you fill tank with city water, do you do so until you get water coming out the overflow?

Sharon_is_SAM · October 2025

Is your problem with draining the tank or with using the pump to draw water?
Good idea @rfuss928!

@Miwok - is there a vent tube next to your fill spout? If you leave the fill cap off, can you drain the tank?

ScottG · October 2025

You have a 2015. Is this a new development? (Or a new-to-you camper?)

Miwok · November 2025

We discovered that the tank has a giant bulge in the back, hanging over the axel. The pump can't get water over the hump. Looking for a replacement tank and coming up short. Does anyone have the dimensions of the 2015 css water tank?

Miwok · November 2025

In answer to your questions: We bought this 2015 css used in 2021. The amount of fresh water was always disappointing, which we thought was our learning how to use water sparingly and to learning how to fill it correctly (getting the bubbles out). Pump was replaced. Then we measured how much we were getting out (2 gallons) and then looked underneath. That's when we saw the tank hanging over the axle. Trying to find a replacement.

ScottG · November 2025

I don't know if all 2015s used the same FW tank, but the one under my non-CSS is similarly deformed over the axle. Doesn't sound nearly as bad as yours, though.

I've never measured it exactly, but I estimate I get no more than 8-9 gallons from my "11 gallon" tank before the pump starts drawing air and loosing prime. I attribute this in part to the deformity in the tank, but I suspect the bigger cause is whirlpooling at the outlet when the water drop below a certain level.

Sorry. Relevant perhaps, but not much help for your specific problem.

ScottG · November 2025

Referencing your other recent discussion I'm thinking maybe the CSS uses the same tank as the non-CSS. Does yours look like the ones in the photos in that discussion? If so, I'd offer to crawl under mine and measure it, but couldn't you do the same on your own trailer?

Miwok · November 2025

I've learned the dimensions are 36x20x4". In looking for a new tank, I'm coming up short. No one I've found makes a 4" high tank. I am intrigued by Scott's suggestion of whirlpooling at the outlet or an airlock. I wonder if unscrewing the fill cap would release the air. . . You all are being so helpful.

Fresh water tank emptying 20%

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