I just bought an 80 year old house on a raised foundation with cast iron drain pipes. I had a drain stoppage on one of my bathroom sinks which I could not unplug. I went under the house and cut the galvanized pipe that led to the cast iron drain pipe. It was clogged with a solid mineral like material. I replaced that short section with ABS pipe.

Should I go about and replace all of the drain piping (both cast iron and galvanized steel) that I can access with ABS drain pipe?

Also when I purchased some 10' lengths of ABS drain pipe they all seem to be curved and not straight. Is there some way to straighten the lengths before I use them??

Thanks for your opinions and help.