long? :) Funny.
The point is that a mild acid has dissolved serious encrustations overnight and a stronger acid wouldn't do it any faster. If you think otherwise, get yourself a tub of sulphamic, which is strong AND safe. Both of your suggestions are anything but. The minute you take the cap off sulphuric it's an accident waiting to happen. It might be ok to chuck the whole lot down a drain to dissolve a dead cat but I wouldn't want to be diluting and decanting the stuff. It's a T shirt I own by the way