What is the WC acronym referring to? And the previous owner installed slate for a bathroom flooring!! Horrible! Eventually this will get gutted and remodeled.
I did a few of the punch through the floor system, but stopped because I became the A hole when people wanted to change their lavs, and my referrals suffered.
I now cut the drywall and cut the galv. below the elbow and remove the pipe from the bottom, feed the new through the same hole, solder the 90, compression angle stop and patch the drywall.