We have a similar unit (Heartland Elevation) and the fresh water tanks have been trouble for us since day one. Ours had no drain at all. Our dealer installed a drain valve for us under warranty, but the small 1/2" valve takes FOREVER to drain the tank and it doesn't even completely drain all the water. I have a hunch that the valve only drains one of the tanks.
Before our last trip, I knew we'd have hookups most of the time, so I opened the valve and let it drain overnight. The next morning it was done draining and I shut the valve. The sensor showed that the tank was 2/3 full (which doesn't mean much to me, since these sensors aren't reliable), but there was absolutely still water in the tank. There was plenty of water for toilet flushes, washing hands, and even a shower. It still isn't empty.
The other issue I have with the fresh tanks is that it's hard to fill them. The vent lines loop back down below the bottom of the tanks, so if I fill the tanks full enough for any water to bleed from the vents, it will siphon 30-40 gallons out of the tanks, which is ridiculous.
Our rig is back at the dealer for this and a list of other issues.
2015 Crossroads Elevation Homestead toy hauler
2014 Dodge RAM 3500 4x4 Diesel Dually