Swivel fitting for Oil Return.
This is an excellent way to return oil to the engine by drilling a 10mm hole dead centre in the oil filler cap. This allows for many options such as, partial oil changes and oil removal simply by removing the cap while the engine is running and allowing the fitting to pump oil into a container. Some diesel owners remove a litre of oil occasionally and put it in the fuel tank. It is then used as fuel. A perfect way to recoup the cost of the oil and at the same time add new oil to the engine. They find that oil changes are eliminated totally.