2021 3121RL: We have had a leak around the fresh tank drain since the day we brought the rig home and filled water for the first time. On a recent trip to Colorado, under a heavy drought, we got a bit fed up with the inability to hold a full tank of water traveling to our next site. So, we dropped the coroplast and had a look:
Issue #1: (see pic) It appears the tank was dropped on the tank water overflow outlet which cracked it across both sides of the spin weld. When the tank got to a bit over 2/3 full (note the 2/3 tank sensor bolt in the pic) it would expand and leak from this crack. Currently relying on some FlexSeal to prevent further leaking (temp fix, but working so far). Troubling, and the next step will be trying to get this warrantied.
Issue #2: the overflow hose didn't seem to be ideally routed it seemed to be exacerbating the crack/tank-expansion when filling as it took quite a bit of pressure to 'burp' the water as the tank filled. Re-routed a bit (less of a drop) and it fills much better with a more normal overflow/output.
Semi-solution #3: to hold a full tank when driving we have started to use a rubber cork/stopper placed in the overflow. No more siphoning and we arrive with all the water. Another item for the checklist, but it works.