Rust in tank

[BSAfrica]

After not having used the bike for a while, discovered some bad rusting in the inlet section below the fuel cap. Decided to take off the cover plate that give access to the fuel filter and pump, just to find some corrosion on it as well, with rust starting in a.couple of places inside the tank. Fuel removed was quite contaminated, seems that water drain pipe was blocked causing rain and waswater to end up in the tank.
Need some advise on how to treat the tank without damaging the paint, also, looking for replacement parts for the inlet and access cover.
Thanks, Barend

 

[BSAfrica]