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Old 10-08-2020, 09:55 AM   #1
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Fresh Water Tank Question

I have a 2021 CC Silverback 33ik. The paperwork says that the trailer holds 69 gallons of fresh water. I assume that includes the 12 gallon water heater thus providing 57 gallons in the tank? When I fill it up, water begins to flow out of the overflow at 53 gallons. I assume that the other 4 gallons is somewhere in lines or who knows? At any event, it appears that I have 53 gallons of usable fresh water. So I head to the camping spot, about 60 mile drive. Upon my arrival, I check the One Control Monitor and it now shows that the fresh water tank is only 2/3rds full. I know that tank sensors are notoriously poor, but I wonder if the sloshing back and forth as you drive, causes water to flow out of the tank thru the overflow tube? This scenario has been consistent all summer. I fill the tank at home. Drive to the campground and the monitor consistently shows 2/3rds full. Is this normal? Do I have a bad valve somewhere? Should I take this back to the dealer for inspection and possible repairs? I appreciate your thoughts. I attempted to add a photo but not sure it actually worked.



Dave
2010 GMC Sierra 2500 HD
2021 CC Silverback 33ik
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Old 10-08-2020, 10:16 AM   #2
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Yes... there have been many reports of the fresh water tank emptying itself on movement of the R/V. Some folks have added a shut-off valve to the overflow line.

I would concur with all your other assessments.

On another note: Even with 53-57 gallons of fresh water, I'd be happy. We only have a 40 gallon tank. Time to trade?!!!!!
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Old 10-08-2020, 10:25 AM   #3
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Quote:
Originally Posted by 5picker View Post
Yes... there have been many reports of the fresh water tank emptying itself on movement of the R/V. Some folks have added a shut-off valve to the overflow line.

I would concur with all your other assessments.

On another note: Even with 53-57 gallons of fresh water, I'd be happy. We only have a 40 gallon tank. Time to trade?!!!!!
X2.
Used to happen to me all the time. My vent tube comes out the bottom of the RV, below the tank.
I put a globe valve on it and close it after I fill the tank to solve the problem. Sometimes I forget to reopen it when I get to my destination, but it causes me no problems as I have a gravity fill port and the cap has a hole in it to provide an extra air vent.
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Old 10-09-2020, 08:24 PM   #4
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On a side note ... you may want to drop the section of underbelly beneath your FW tank and add or modify the holding straps if you plan on traveling alot with the FW tank full. Straight from the factory, the straps are minimal for supporting #440 of water. I've been under there face to face with the OEM setup. There is a molded step designed into the tank that lets it sit on cross members, but not a whole lot supporting the tank bottom.
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Old 10-10-2020, 04:35 PM   #5
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Not only sloshing

Quote:
Originally Posted by 5picker View Post
Yes... there have been many reports of the fresh water tank emptying itself on movement of the R/V. Some folks have added a shut-off valve to the overflow line.

I would concur with all your other assessments.

On another note: Even with 53-57 gallons of fresh water, I'd be happy. We only have a 40 gallon tank. Time to trade?!!!!!
It's been suggested that the problem is not only due to water sloshing up through the vent during movement, but that you can have actual siphon action.

The siphon principle: Remember that you can set a full glass of water near the edge of a table and insert a piece of flexible tubing into it, to the bottom. Drape the other end over the edge of the table and give it a quick suck to fill it with water. Water will flow until the glass is empty, even though that flow is uphill from the current water level to the rim of the glass. This is because the weight of water in the uphill portion of the tubing is less than the weight of the water in the downhill portion.

Now, put that tubing in the full glass, but only 1/3 of the way from the top and start the siphon. Water will flow, but once the water gets below the bottom of the tubing in the glass, no more can be drawn.

Now that I've gone through this tedious example, it will be obvious to you that the problem is that the overflow tube in your tank is sticking down too far into the tank. In fact, it is sticking 1/3 of the way into the tank. You need to extract it until it is barely into the tank. Hopefully there's a way for you to get to it without dropping the tank.
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Old 10-10-2020, 04:45 PM   #6
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At least on my Silverback, there are no internal tubes in the FW tank . There are several fittings on the plastic water tank spin welded on. Each line whether fill, siphon, drain, or vent/overflow attaches directly to the respective fittings. It's quite likely that the vent tube is not looped high enough above the fresh water tank to break siphon . You might check and reposition the vent/overflow hose so it is about a couple inches higher than the tank before it drops down below the belly pan.
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Old 10-10-2020, 06:36 PM   #7
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This happens with our 2021 Wolf Pup trailer too. For some reason Forest River decided they didnít need to attach a hose to the over flow tube so water sloshes out while traveling.
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