The discharge seacock needs to be closed at all times inside the "no-discharge" zone, which varies. In addition the discharge pump should be locked out. USCG Marine Sanitation Device (MSD) Regulations They can ticket you, but not likely. I suspect the discharge thru hull is filling the tank. Closing the seacock solves the problem, but to discharge you'll need to open the seacock and run the pump. There are other threads on the forum regarding the regs. ie. "Discharge Rules."
