Flushing Old Fuel?

I'm buying a boat with a 1996 Johnson 88 engine, a 2-stroke, and the fuel might have been in the tank for more than a year. It's about half a tank.

The mechanic said it's strongly advisable to flush the old fuel. The salespeople, of course, say it's enough to just add some octane booster. They say, try it in the water and see if there's a problem first. But I wonder, if that's bad for carburetors, as the mechanics says, wouldn't it be too late to see that you might have a problem?

Is there a good rule of thumb to ascertain whether flushing is necessary?
If it is, what's the best way to do it -- are there any useful tools to get?

 

Old gas + fiddly carb = bad
Gas does go bad, especially if it wasn't stabilized with the proper additives before storage. When it does, it can gum up the fuel lines and jets. Probably easier to just flush it, then have to tear down the carb when it clogs. The mechanic knows how it works and how to fix it, the salesman often just knows how to sell it. Who do you trust when it comes to making sure it works?

 

Thanks Matt -- now, if the salesmen are unhelpful, and the mecahnic says it's more expensive for him to dispose of the fuel than a new tankful costs, what's the most efficient way for us to do it? Is it just a tube and a canister to siphon it off?

 

ask for a fresh tankfull, could siphon, a vacuum pump for carters can also be helpfull, drop the hose to the bottom were debrie and water collects