1972 Volkswagen Beetle Oil.

remove the plug in the center of the circular plate on the bottom of the engine. Drain the oil. Remove the plate (10 mm wrench for the nuts around the edge). Remove the wire strainer and clean. Reassemble and top up with oil. Sorry, I forget how much.

There is also a gasket that should be replaced if you don't want any leaks, but it's no big deal if you reuse the old one. Just be sure to have the valves adjusted every 6000 miles or so.