Motorcycles, Snowmobiles, Go-Carts, ATV's and Golf Carts - moped gas tank

I have an old motobecane moped that has been sitting for a while with little gas in it. The gas tank has rusted on the inside and i cant take it off because it is just a wide spot in the frame. I tried pouring a gallon of gasoline through it and got some out. I also put a fuel filter on it but there is still a lot of rust in it and i can see it in the gas line. Ive been told that if i fill it with deisel and leave it for a while it might get some out. Is this right and what should I do?
Thanks

Hello Butterfingers!

It's odd that they would make a non-removable tank. I would try to remove as much rust as I could by flushing it with gas. Then install a large fuel filter that has a transparent housing so that you can see when it gets full of junk. Then you should be able to run it, and just keep an eye on the filter so you can replace it when it needs it. Maybe keep an extra on the bike somewhere. I don't see where diesel fuel will do anything.

I've had success cleaning rusted fuel tanks with liquid Drano. I would drain out any fuel and add enough Drano to fill 1/4 the tank and swish it around, let sit, repeat. It seems to eat up the rust and gunk. The only problem I've run into is when the tank is rusted to the point that it begins to leak after it is cleaned out.
Also, one guy on this forum tried "goof-off" a kind of solvent/paint remover and added some small pebbles into the tank for the abrasive, shook the tank around with the solvent/pebble mixture and was pleased with the results. This might not be easy for you if the tank is part of the frame.