Contaminated fuel tanks
If you have a badly contaminated fuel tank you should be able to treat it and not clean it out. Use a shock dose (100ml to 100 ltrs of fuel) of Marine 16 Diesel bug treatment, stirring in if possible. Leave for 72 hours and then add Marine 16 Diesel Fuel Maintenance at 500 ml to 375 ltrs. The Diesel Fuel maintenance will increase the cetane rating of the fuel and clean your injectors and fuel lines. This should enable the engine to run normally without worry. The sludge build up in the tank may take a couple of doses of Diesel Bug treatment to fully break up and disperse but it is a lot cheaper and easier than removing and cleaning a tank.
Remember that if you do opt for tank cleaning one remaining organism in the system can kick off contamination again so use a regular (100ml to 2000L) dose of Diesel Bug Treatment to ensure you never have the problem again.
Fuel oil heating systems
If you are lucky enough to have on-board heating you can get starting problems due to degradation of diesel in your tank. Some manufacturers recommend the use of a separate tank for heating but this is not always possible. One of the problems for poor starting is the loss in performance of the diesel on storage. This can be rectified by using Diesel Fuel Maintenance at the standard rate.
Smelly holding tanks
Often the odour from holding tanks is cause by migration of the contents through the polymer. Spray the header tank itself with bilge deodoriser sanitiser and it should help keep the nasty niffs at bay.