On any trailer, the dump valves and related plumbing will eventually require service. After 4 years, mine had a leak.
Other threads here have pointed out that it is a mistake to remove the belly pan for this repair. Instead, it is much easier to cut an access panel in the belly pan, below the valve area, and place a removable cover over it when the repair is complete. The main trick in doing this is to avoid damaging the tanks and plumbing.
I purchased an inexpensive air shear for this job, and it made it much easier and reduced the risk of damage. By looking through the holes for the dump valve handles, it's possible to identify a safe location for drilling a starting hole. Unlike tin snips, the air shear cuts without distorting the metal. Unlike a saw or cutoff wheel it barely penetrates above the sheet metal and won't damage the pipes and valves. They do only cut in straight lines.
Photo below is of one of reasonable quality. I got a cheap one at the closest home center since I don't anticipate using it much, and it worked ok.
Oh, and the leak? Two loose hose clamps on a 3" rubber coupling.