My underbelly got full of water one time when I was filling the fresh water tank, and at the time, I filled it by inserting a garden hose into the fill hole, and left it unattended
The garden hose fits rather tight into the fill hole, so I depended on waiting until water came out the overflow vent to determine if the tank was full. It turns out that water goes into the tank faster than the overflow can handle, and it leaked out the overflow hose fitting at the tank, and into the underbelly.
I now have a fill adaptor that screws on the fill fitting, but has large holes to relieve pressure as it fills. It also has a shutoff valve at the tank end. I now monitor the fill, and stop when I hear it coming up the fill pipe.
Doug and Patience and Shelby the mutt
2015 Crossroads Sunset Trail Reserve ST26RB
2013 Ford F-150 3.5 EcoBoost XLT Supercab 4x4