black water tank leaking

I know I would drop it off at Camping World and say Fix It and clean it. But if you must try yourself cut a hole dear the center like a flap with the "hinge" part at the front of the flap. Open both sides of the belly pan some so you can get a hose in it and begin to flush it out. Its gonna be stinky and messy. Now you need to find the leak. You may have to drop the entire belly pan or part of it looking for a leaky pipe or cracked holding tank. That will determine your next step. Cracked pipe you might get away with cutting another flap and fixing it. Cracked or leaking holding tank requires a patch or replacement.

Either way you go its gonna be a crappy job for someone to fix and clean.