When you open the drain on your Racor FG500, a little diesel
(or whatever lies at the bottom of the filter) will drain -then stop. If you need more to drain, you will have to open the top which will allow the full contents of the filter to run out. Fuel will run back down the in coming hose if the filter is higher than your tank if you can't shut off a valve at the filter inflow. If you fill the filter up to the top with fresh diesel, seal the lid, and then manually prime the fuel pump
, on the Yanmar
2G, you can probably get by with out a full bleed. Let the engine run for 15 minutes or so before heading out to make sure you have no air in the fuel line. If the engine dies, simply start the bleed process at the secondary filter.