I have a somewhat grotty old 3/4 threaded hub on a galvanized steel fitting and I need to thread a new 3/4 brass fitting into it. The old threads are not particularly nice, but they are likely serviceable. Is there a standard procedure for cleaning and dressing an old rusty, putty-encrusted fitting to take a new fitting and make a good seal?
I was thinking of getting a 3/4 black pipe nipple, cutting a slot across the threads (like on a self tapping screw) with a grinder and using this to run into the old hub to clean up the rust and crust. Kind of a home made chasing tap. Is there a better way?