Dont cut your under belly with a knife. It should be put on with screws. Mine has square drive screws holding the under belly up, so I just remove those to access anything.
The water may be coming out just because you are over filling your tank.
2012 Jayco Eagle 321RLTS
2008 Dodge Cummins 3500 DW Crew Cab 4x4 6 speed Auto, Exhaust Brake