[carisea]

I would assume you would have a tank cleaning service in your area. I had this done recently because of a slime build up on my primary fuel filter. process continually recycles diesel fuel forcing fuel back into tank under pressure thus blowing gunk and water into suspension in diesel fuel then mixture is filtered extracting water, gunk bioslime until diesel is clean and tank is clean. Some services only filter the fuel if they do not force fuel back into tank and jet the sump you will still have a dirty tank with clean fuel