Jim, What tank cleaning costs varies widely depending on how it's done and where. One day? Depends on the level of contamination and size of the tanks and the approach to cleaning the tanks. Before I replaced the leaky fuel tanks on my Grand Banks in the 1990s I learned that there are several ways to "clean" fuel tanks: 1. Agitate, filter and return. The most common and least effective method is to use pumps, hoses and sometimes compressed air to "agitate" the fuel in the tank which is then pumped through a large filter and immediately returned to the tank. The aim is to get all the stuff at the bottom in suspension, then filter out what's there. This works OK is you've gotten a bad load of fuel and are dealing with it soon after taking it on. For a more longstanding problem, especially on on older boat or one that hasn't been used much, the problem with this approach is that you never get a truly clean fuel tank because much of the crud remains caked on the bottom. That's because the baffles in the tank will not allow agitation of all the fuel in the tank--the baffles interrupt the agitation process. While this method may result in cleaner fuel than before, personally I believe it's a poor substitute for cleaning the tank the right way. 2. Remove and filter all fuel, then return and filter all fuel. Pump all the fuel in each tank out through a filter until the tank is empty, stowing the fuel temporarily in a tanker truck or portable tank. Then pump it all back into the tank through a clean filter. This works fine if you've gotten a bad load of fuel, but it's not the answer for a boat with a longstanding fuel problem with lots crud at the bottom of the tanks. 3. Remove and filter all fuel, physically clean tanks, return and filter all fuel. Follow #2 above, but once the fuel has been removed open the inspection ports and, using a hoe and scrub brush and other tools, go over every bit of the bottom of the tank to loosen the crud, then spray it down with some of the diesel removed, pump it out and dispose of it. It's crucial to get every corner of the tank, sometime often impossible through a single inspection port. No inspection ports, you say? You can add your own using the excellent ready-to-install kits available at: http://www.seabuilt.com/ 4. Inside job. Nordhavn is one of the few builders with fiberglass fuel tanks, each with a "man-sized" access at the top which allows someone to get into the tank and clean it. All baffles are removable, so it's easy to get to the corners of the tanks and easy to see when the tank is truly clean. Fortunately for me, that hasn't been necessary in five-plus years of ownership--the fiberglass tanks produce virtually no condensation, and in my experience water seems to be the beginning of most fuel contamination problems. One final thought: it may be best to determine the source of your problem and deal with that before cleaning the tanks. Usual yadda-yadda: no connection with Seabuilt, just a very satisfied customer. And very satisfied Nordhavn owner who is a sometime consultant to Nordhavn. Good luck, --Milt Baker, Nordhavn 47 Bluewater, Fort Lauderdale Can those who have had their fuel tanks cleaned (sludge and/or water) give me an idea of what this process costs? I assume it's done in one day. Is it easy to find vendors that do this work? Is it done by the job? By the gallon? by number of tanks?, etc. Any experiences or information is appreciated. Thanks, Jim