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Recently purchased an 85 Outrage that had been sitting for three years.

The engines are all cleaned and tuned and ready to go but I have only run them off external tanks.

The internal tank is reading 'empty' but I am sure there is probably at least a few gallons of old fuel (mixed with oil) in there as well as varnish and 'crud' from year of use and sitting.

My question is how do I clean out the internal tank?

Here is what I have come up with so far:
1 - remove the tank, cut it open, clean it, weld it back together and re-install it. This would work. It would also be incredibly expensive and a complete waste of money and time.
2 - put 10 gallons of fuel in the tank. Let it sit for a few days so the ethanol can 'clean' the tank and then pump it out by hand and use it in a car.
3 - just put gas in the tank and carry 3 extra fuel filters in the boat for when they plug up.

I cant be the first to have had to deal with this. Any help or experience would be greatly appreciated.

Graham