Lay the compressor on its side and take a hacksaw blade and make two cuts 180 degrees apart in the brass fitting just down to the threads. Then take a small chisel and peel the remains of the fitting out of the tank. Removed a number of large brass fittings like this. Just don't get carried away with the cuts or you'll have another problem.
i have done this as well.
if you have an air saw, that will make the job easier.
as to the brass becoming brittle, causing it to break, the actual cause of the break was that the brass had galled to the steel threads.
repaired many fittings because of this in my 45 year machinist career. the cause was always galled threads due to dissimilar materials. even using teflon tape or paste will not rule out this possibility, although it does reduce the chance of breakage somewhat.
