Hi,

If you have a problem with a bit of rust and trash in your fuel tank and are prepared to remove the tank, you may want to consider a tank sealant.
If you go to a good motorcycle shop and ask for the sealant package, I forget the name, but it comes in 3 bottles.
The first neutralises the rust.
The second coats the inside of the tank with a flexible fuel proof coating.
The third neutralises the others and sets off the coating I believe.
It takes a few hours and you have to turn the tank around regularly but it does a very effective permanent sealing of the tank.
The pack costs about $30 and you may need 2 packs because of the size of the tank but it will enable you to keep your original tank and not have fork out for a new one and deal with different filler sizes etc.
Just stop by a motorcycle repair shop and ask them about it.
I have done it on 2 vintage bikes and was very satisfied with the result.

Good luck,
Steve Cotsford