Regarding fuel tank cleaning and polishing:

If you have one microbe left alive in your system, it will grow again. Cleaning the tank and polishing the fuel WILL NOT result in a clean system, just a cleaner system.

You would have to completely disassemble the entire fuel system and clean each part thoroughly, including using compressed air to blow out the hoses and line and all components, and even then it is impossible to get it 100% clean. The slime is just too slimy.

I know because I paid for such a service on a Volvo diesel I used to have. It did NOT leave me with a clean fuel system, just a cleaner one.

Might be a good idea to clean out your tank. Might be worth paying $500 bucks if you end up with inspection ports and you don't like doing dirty jobs yourself. But it will not result in an algae-free fuel
system. No way. Depending on how it's done it could release a bunch of gunk downstream into your filters so make sure you have a bunch of replacements.

You can "polish" the fuel yourself by running the fuel lift pump (turn the engine to 'on') and allowing it to circulate your fuel  through your Racor filter. It takes a long time. You can speed it up by running the engine in idle. This is excatly what a fuel polishing "service" does. They might have two Racors in line. But it will not result in an algae-free fuel system. No way.

Therefore your continued maintenance program of using Biobor and draining the water from your Racor filter is the most important thing you can do.

In general, a fuel polishing "service" is a waste of money.

I tend to agree that fuel polishing "services" are a waste of money. The only way to really clean a tank is to physically get in there and wipe it clean by hand. For the money, on a small tank, you are often better to simply suck out the dirty fuel and give to someone with a waste oil burner or oil furnace or boiler.. Then go in and clean the tank by hand and re-fill with fresh clean fuel. There is little sense in paying hundreds of dollars to "polish" $65.00 of fuel.....

Once that is done if you install an on-board, high turn over fuel polishing system, the cost in under $300.00 and can be less than $100.00 if you get creative, the tank will stay clean for many, many years. I will never again own a boat without an on-board fuel polishing system. Our tank walls and bottom are 100% spotless and the fuel is crystal clear...

In an ideal world the polishing pick up dip tube would get within 1/8" of the lowest part of the tank and the return tube would be within 2" of the bottom of the tank on the opposite side. If cleaning the tank you can simply remove it, drop it at a welder and have them install extra tank tappings/bungs for a polishing system...

That said investing $475.00 on an 86 tank is a risky move in and of itself. The design and install of these tanks was horrible, they sit on plywood and the tank can rot out from entrapped moisture between the plywood and aluminum.. A brand new tank can be fabbed up for far less than the cost of the fuel polishing and tank clean out. You can also order as many tank bungs as you want such as one set for teh engine, one set for fuel polishing and another pick up for an Espar or similar...

We owned an 86, tank leaked, ordered brand new from Catalina for under $300.00 delivered to Maine. Course this was years ago but still $475.00 on an 86 tank may not be the best way to spend the money, for others reading this or thinking about this issue........

Hello all,

I had the fuel polished on my '86 MK 1 about one month ago for the first time since buying the boat in 2007 (a little over 7 years). The tank is original and there is no inspection port for cleaning. When I purchased the boat, I think the tank was fairly clean. I never had a filter clog and the filters themselves always seemed clean when replaced. Periodically, I stuck a small hand pump into the tank from the fuel sender port and pumped out some fuel from the bottom to check for water and sludge. Typically, it was always clean. Over time, however, I began to notice algae accumulating on the plastic filter of the lift pump and more residue in the sight bowl of the racor so stuff was starting to build up in what was a clean tank. I opted for the fuel polishing before things got bad. It was simply the most expeditious thing to do without another "boat project". They did it without my being there and replaced all the filters. I'm sure it helped clean the tank. No issues since then. I was a little skeptical myself whether it would do any good so I asked the owner of the polishing service what I could expect. His reply is below and I think it is an honest assessment.

Fuel polishing for your tank involves removing the sender pumping out 
most of the fuel, leaving just enough to circulate in the tank. We will 
be able to remove the majority of the 'crud' in the tank. Fuel polishing 
is not tank cleaning, it is a dialysis process. Anything that can be 
loosened from the surfaces with the return fuel will be filtered out.  
Tank cleaning requires a access port or ports. Your tank is vary 
accessible and we will be able to get most of the debris out.
There is no need for you to be there. All we need is access to the 
boat, the location of the key for the engine, usually in the chart 
table, and a phone number in-case we need to contact you.

Regards,
John