If your water tank is like my 2008 then the water tank has a Rotocast cover. The actual water tank is supported by this cover and Styrofoam blocks inside. The water drain exits the tank to the street side outside valve with a short tube. To replace that tube you would have to cut an access hatch in the bottom of the Rotacast lining.
The holes in the Rotocast shell is to allow any water to drain from within the shell. I had a small water leak from a connection above the floor hole where pipes come up from the tank. Water collected in the shell and it dripped out from one of the middle holes. I was worried I had a leaking water tank but after repairing the connection above the problem was solved. I also noticed the water pump would cycle on/off after about an hour indicating a plumbing leak.
Since your description indicates leaking from the curb side its either the water tank leaks, the water fill hose may not be tight and when filling the tank water gets into the shell or the water drain hose is leaking and somehow in the shell its leaking out the curb side drain holes. I would think the 2013 25fb modes still have the drain on the street side between the wheels but may the water is still drain via the curb side.
2008 Classic 25fb "Silver Mistress"
2015 Ram 2500 6.7L Cummins. Crew Cab, 4x4, Silver
2010 Tundra 5.7L, Double Cab, 2wd, White