Had the same worries about the fuel system with both the 3800 and 4400. Things didn't turn out to be so bad. The 4400 hadn't been started for 12 years, so I was very suspicious.
The first thing I checked was that none of the fuel line connections leaked, so I just poured a gallon of gas into the tank and got under the truck with my BIC ;} (NO WAY!)
No leaks, so I disconnected the fuel line at the input to the fuel pump and let the fuel run into a bucket. After it quit dripping, I put another bucket under the fuel line and dumped the first bucket back into the tank.
After three rotations with the old stuff, I started using fresh fuel. One of the things I was looking for was that the same approximate amount of fuel came out as I put in. Maybe I was hoping I would get more out than I put in due to the current price of gasoline.
So the tank and the tubing to the fuel pump appear to be fairly clean since there was no residue in the buckets.
Now I have a clear plastic filter in the tube that feeds the carburetor. Remember to keep the carburetor end of these filters as far above the fuel pump end as possible, because the gasoline will float on top of the water. If there is a lot of water in your system, the bottom of the filter fills up with it until you're getting water overflowing into the carburetor. That will make your truck run poorly, if at all.
Next step for me is a metal cannister type filter between the tank and the fuel pump. I figure I'll change them about every month for three months, and then once a year after that. The cannister filters have pretty good capacity. When the truck bounces around, it may knock some rust flakes loose from the inside of the tank. I'd rather not have them get into the fuel pump, which has a rubber diaphragm.
