As a side note, the old man I purchased my 65 F100 from decided to add lead pellets from shotgun shells to the fuel tank every couple of months. When you turned corners you could hear all the lead shot moving from one side to the other. I didnt figure out what it was for about a month after purchase. Very loud. Old truck has metal tank behind the bench seat. I thought is was some kind of vent or fan or something for a while......
I look back at that and laugh now!
There could be another reason for this Mike.
While I was working on my boat, I syphoned out the gas tank as I knew it would be out of commission for a while. There was still 1/2 to 3/4 inch of gas in it that I couldn't get out at the time. When I started wetsanding and buffing the hull (after the small amount of gas in the tank had sat there for 3 years), I had to remove the tank to remove all the hardware on the transom. When I looked in the tank, there was just this ugly goo that was laying in the bottom of the tank. I looked more like molasses than any kind of fuel?

I started calling around to find a place to clean the tank as radiator shops used to do this. No more with the stiff mandates from the feds I believe for the caustic cleaners that they always used. I heard from several old timer motorheads and speed shops to throw a gallon of mineral spirits in it with a handful of nuts and bolts

and shake the hell out of it. Are you kidding me?

they said they do it all the time to clean out rusted tanks.
Well, I knew my tank wasn't rusted and I only ended up putting a gallon of mineral spirits in it, shaking it up and letting it sit for a couple weeks. It cleaned it out perfectly.
That old timer could have very well been putting the BB's in it to keep the steel tank clean. Just a thought anyway.