Diesel bug bacteria grows at the interface of water
and fuel, prevention is better than cure so simply keep the water
out ! drain any water from the tank via the tank sump,, if you have no drain then look for the fuel gauge, if it's on one side of the tank, remove it, then careen your boat and let it stay in that position overnight if possible,if not minimum 6 hours, so the any water in the bottom of the tank will drain to the point just below the fuel gauge opening, get a hand pump, some lengths of clear pipe and a container, insert the pipe into the tank and VERY VERY slowly start to extract the crud/water from your tank until clear fuel flows, reassemble the fuel gauge. It's a hassle I know but prevention is much much better than cure. Some folks thought it very funny
when I posted to ask for a sample of fuel when filling, this is particularly important when cruising 'off the grid' as they will often give you dodgy fuel to get rid off it knowing you won't be back.