What's the best way to restore a fuel tank that had fuel sitting in it for four years?

Thanks in Advance

I have heard of a survice in FLA they would drain, flush your tanks and tell you there capasity. Never used them.

The best thing to do is find a service company in your area that provides fuel polishing (speak to nearby marinas). They perform what could be described as "dialysis" on your fuel and tank. They have a portable machine that will suck the fuel through 1 micron filters and create a jacuzzi effect that will agitate and get out all the sludge and particles (including any water) out of the tank.

Approach would depend on how much fuel is there, and how old the boat/tank is. Pull a separator off and pour out it's contents into a glass jar or bowl to check it's appearance. If not too bad, and if very little fuel in the tank, then pickle it with Pri-G, Startron., and Stabil. Then put fresh gas in and run it out topping off frequently with more fresh gas and changing fuel separators every 3-5 hours until the fuel shows up clean. Then keep topping off frequently to continuie to diminish the old to new ratio.

Syphin out some into a gas can and do the glass jar/bowl test first. Make your judgement call from there. If it's 4 years old chances are "maybe" it's not Ethanol improving your odds.

I have an electric fuel pump maybe I can pump it out and see how bad the fuel is first.

I dont know where on the water you are located but here in Palm Beach County Florida we use a guy called Dr. Clean Fuel. He pumps it out polished the tank and you are ready to go when he is done!