Easy Way To Flush Out A Converter?

And the second best is to put it on a flusher, then next would be the drain plug.

But yea, the drain plug works if it doesn't have metal in it from something blowing up.
Works best with compressed air and solvent, then blow as much of the solvent out as you can put a quart of new fluid in it till it's used.
If any metal went through it don't risk it because it has already scored the bearing surfaces.