A marine tank (such as a toilet system holding tank, or bilge tank) pump out system includes a positive displacement pump connectable at the inlet to a marine tank to be pumped out and connectable at the outlet to a discharge tank or area. A pulsation dampener is connected between the pump outlet and the discharge tank or area, preferably directly to the pump so that a pump check valve is within the pulsation dampener. The pulsation dampener has an open chamber extending upwardly from the pump outlet into which pumped fluent material may flow, and has no moving parts (such as a diaphragm). Typically two different outlets from the dampener are provided for versatility and connecting up to discharge tanks or areas, one of the outlets filled with a plug. The dampener may comprise either a substantially L-shaped or C-shaped (when viewed from the dampener inlet) casing, which nests with the pump motor.