If no water/diesel interface line and no dirt, you are good to go. Opening the drain tells you nothing additional.
Be sure to use the right micron rated filter(S).
If just one fuel filter (the water separator/fuel filter) the micron rating must meet the specs for your engine-- generally 2-5 microns.
If you have both a primary (water separator/filter) AND a secondary fuel filter, then the primary needs to be between 10-30 micron and the secondary the correct spec for your engine.
Ex: 2003 Alpine 38FDDS. Ex: 1997 Safari Sahara. Ex: 1993 Foretravel U240