Okay. I made up this problem in my head. Sloshing is a non-issue with a set up like this.
We did a 5 night trip in Moab where we bounced around as much as I will ever. I started with 12 gallons and ended with about 1 or so. I never one single time heard or thought otherwise of any noise coming from the tank. Just the pump when using the water, but that just made me smile, it wasn't loud.
This is very unexpected (obviously) as my other portable plastic tanks made a lot of noise.
Perceived problem, solved.
1999 Land Cruiser ::::: ARB front - Warn M8000 - 3rd cup mod - Rear no-bumper? - 295/75/16 BFG AT - Cobra CB - OME lift w/ 863 rear coils - lots still to do!
2000 4Runner: sold...and missed