I installed a Racor 500 MA fuel filter with a vacuum gauge, between the fuel tank and the engine, mounted in the engine compartment in an easily accessible place, with its own shutoff valve, so it's easy to change the Racor filter. This becomes the primary fuel filter on my Yanmar 4JH3E engine on my 2004 Hunter 41. The secondary fuel filter is part of the engine (very fine filtration, 2 microns) and is mounted at the engine at the injector pump. Yanmar recommends replacing the secondary at 250 hours of engine use, but of course it's easy enough to check periodically. Mack Boring, the largest Yanmar dealer in the US, recommends a 30 micron element in the Racor (color coded red). The vacuum gauge tells you when the fuel filter is ready for replacement. This eliminates guesswork and replacement of the fuel filter too early or too late. It also keeps the secondary filter, on the engine, sparkling clean. It is a simple matter to drain the Racor of water and other large impurities after each day of engine use. The water and big stuff fall to the bottom of the clear bowl. No tools necessary, just a hand tightened valve at the bottom, also no need to bleed air out since none enters when you drain it. When I checked the secondary, it was crystal clear and clean. Not a lot of money for protection that provides lots of peace of mind on a critical engine system, i.e., clean fuel. Keep the fuel tank full and buy fuel from a dock that pumps lots of fuel. You should check the vacuum gauge when the engine is under load. I bought the vacuum gauge that records the highest vacuum reading, so I don't have to look at it while the engine is running. I can check it at the dock and the needle will tell me the highest vacuum pressure that was reached. Easy to do and highly recommended.