21g gravity fresh water fill

[schoonod]

This conversation has been interesting in that I am not the only one having an issue with the Grand Design layout. My 2019 25G water system is just like Megan's. No way to gravity fill the water tanks. I have a small hand pump and a bucket for adding water to the tank if needed for longer boondocking trips. My bigger "issue" is after filling the 2 water tanks and driving to the camping spot, water comes out the overflow tubes during the drive. I haven't checked how much is lost during the trip but have read some blogs on ideas for how to fix the situation.

[Cate&Rob]

schoonod
I see this is your first post . . . welcome to our owners technical forum.

The situation that you describe has been discussed at length with a few different solutions.
The problem is that as the water sloshes back and forth in the tank while towing, this action "pumps" the water out the overflow tube.

The simplest solution is to put a valve on the overflow tube. The caveat is that you have to remember to open this valve for both filling the tank and using water from the tank.
There are more complex solutions that involve ways to raise the vent/overflow height enough that the sloshing can't pump the water out.

Rob