Peggy, We have a 1999 H380. The holding tank is in the aft port transom locker. The vent line is almost vertical. I would like to install an additional vent line for a horizontal run to the hull with a minimum of surgery. I can access the top, aft of the holding tank without removing it from the locker. Are there "standard" parts available to make this modification? Or am I faced with replacing the holding tank? s/v NEVERMORE