Water Siphoning from Full Fresh Water Tank

[Guest]

An even better solution would be to run the tank vent to a higher location such as the vent port at the gravity fill (for trailers that have a gravity fill). This has been previously suggested on this forum . . . maybe even somewhere in this 8 page 120 post thread . Grand Design is now also considering this, for trailers with gravity fill provision.

Rob

I actually have a seudo design in mind Rob with a combination shut off and supplemental vent in case the shutoff would be forgotten. I have all the parts (including a locking gravity fill) but having my rig stored away from our home provides a challenge to getting things done. To have a high mounted vent would work best but its too much trouble to add the feature IMO.

For trucks, we commonly baffle vehicle fuel tanks but this is mostly done to prevent sloshing noise at stops. RV tank sloshing may also accelerate tank wear in its mounting since they sit loosely in the frame unlike a vehicle fuel tank that is held firmly in place.

Jim

[TedS]

GD should consider putting the vent port centered in the top of the tank. Sloshing is least effective there and no chance of so-called siphoning. Then the vent tube could exit either high (best place) or low (current place). And gain use of full tank water volume instead of current loss of one to two inches from the top., 5 to 10 gallons.

[Saxles]

Ted, when I started to reconfigure the vent line I wanted to elbow the line up to get over the top of the tank. However there wasn’t enough room for the elbows; even though the tank is not tight to the floor.
What I ended up doing is running the pex line to the rear of the tank, putting two elbows on it and running it back to drop down in the original location. The line running rearward was installed with a rise so it ended up tight to the underside of the flooring. Because of this I am now able to completely fill the tank as the line ends up higher than the top of the tank. This gained me 6 extra gallons and my ‘full’ indicator comes on for the first time ever. Hope I’ve explained this clearly.

Anyway the extra 6 gallons is a welcome addition as I know from experience the pump will start to cavitate shortly after the 1/3 light goes out. I have measured the amount of water to get to the 1/3 mark and it is 31 gallons. I estimated that we were only able to utilize about 17-20 gallons of capacity between the sump line being high and the vent line 1 3/4” down from the top.

Last year I ran a pex line from the tank up through the floor into the kitchen island. The intent was to use this for a vent. However I needed to remove the coroplast over the axles to be able to attach the line to the underside of the flooring as it hangs down and would have water lying in it. I just didn’t have time to finish doing that. Maybe I will look at that again some day. Anyway the line is there, not attached to anything.

Honestly the dual drop lines have solved the siphoning problem. I really don’t mind using the manual valves.

I am now thinking of relocating the pump line (maybe get a fitting spin welded in the bottom of the tank?) to be able to utilize more of the bottom capacity of the tank. However that’s next years project. Wife has a long list I need to get through.

[Cate&Rob]

Saxles

From the Grand Design parts information https://www.granddesignrv.com/owner-...s/detail/37171 your water tank should have the water pickup in the small sump at the lowest part of the tank. This should allow you to completely drain down the tank with the onboard pump.

Rob

[Saxles]

This is not where the pickup line is located on my tank unfortunately.

[mtd1899]

I have a 2023 17mke
It loses 1/3 tank of water on a interstate highway drive.
On a 200 mile Montana back road drive it lost 2/3 of the water
Ideas?