Discuss Bob Suffolk's answer to: # 48 propane orifice

I believe that a #48 bit is about .078" and will clean out your hole.  However, even if the tank is drawn down to where the regulator will not give you any more gas, it is still under pressure.  Since 1980, all American pressurized fuel containers have used left-hand threads, while oxidizer and noncombustible gasses use right hand threads.

Even if you have the right tap to chase out the thread, that old tank may not be refillable.  Drilling on pressurized fuel tanks requires specialized equipment and training to do it safely.  That is not a do-it-yourself project.

Propane distributors will usually provide you a certified tank if you agree to buy fuel from them.  That is usually the best way to go.