Modern PVC drain pipes have reduced the number of blocked drains substantially.
This old house in downtown Dayton was built in the early ‘50’s had a sixty foot run to where the blockage was in 58, again in ‘66, ‘03 and ‘06. These were all bad years for this houses main drain according to the Motor-Mole old advertising pinned to a basement rafter with the service dates written in pencil.
Cast iron piping was the norm up to the end of the 1960’s, the joints were prone to leaks which trees planted close to the pipe would find and grow roots into the pipe looking for a constant supply of water. As the trees flourished the root ball in the pipe becomes bigger, still allowing water to flow through. As the root ball grows and the pipe rusts the pressure will often split the cast iron pipe.
Cast iron piping should be considered old and at the end of its useful life, buyers should budget for its possible replacement should the drains get blocked.