Fuel filters can be defined as pre-tank, primary, and secondary. A pre-tank filter would be a funnel type that provides basic filtering of the fuel as it is poured or pumped into the tank. This type of filter is very basic but very valuable. They range from a plastic funnel with a screen in the bottom to catch dirt, leaves, and large contaminants such as bits of plastic, to the more sophisticated Baja filter. The Baja filters are aluminum funnels designed for cruisers who travel remote cruising grounds such as the Sea of Cortes, adjacent to Baja California in Mexico, where fuel is scarce and supplied in used 55-gallon drums of dubious origin.