[gwilli]

When you say bugs do you mean fungus which loves diesel fuel particularly in warm climates? If it is the latter, the fungus grows on whatever the fuel touches including the air space above the fuel on the sides and top of the tank. You can kill it with biocide but the latex-like layer remains and it continues to break-up (because it''s dead) and recontaminate the fuel and plug your filter. The only recourse is to install a gasketed top access flange/door that will allow you to get your arm and/or a brush in and give the inside a good cleaning. Perhaps the nozzle of a high pressure sprayer could be inserted instead but remember the top and upper part of the tank must be hit as well. There are some industrial spin-type spray nozzles for tank cleaning that might do the trick too (Spraying Systems, Sprayco). The problem with spray down is keeping the wash down water out of the fuel (disconnect and plug) and then complete drain/pump-out and dry. We went the clean-out door route on a Westwind Vagabond 42. The moral of the story - use biocide/fuel conditioner in diesel - always!