The oil tank is usually mounted on the engine; it may be a separate unit or part of an external gearbox called the sump. It has provision to allow the system to be filled and drained and a sightglass or dipstick to allow the oil contents to be checked. Usually, the oil level sightglass on the side of the tank is graduated in half-pint or in litre increments, between LOW and FULL marks. The tank is replenished either by pressure or by gravity feed. The pressure filler connection contains a non-return valve and a bayonet adapter to which the oil replenishment trolley pipe is connected.
A de-aerator tray is mounted in the top half of the tank and receives the return oil from the scavenge pumps. The oil in its passage through the system will become aerated and steps must be taken to remove the air. As the oil/air mixture flows over the tray, the oil separates and drains down into the sump, whilst the air is vented to atmosphere.