Water coming out? --Don't let anyone flush toilets or use sinks while you work---
Gas? Cloths pin on the nose?
Don't try cleaning out the pipe like you described---you could clog the lateral line with the crud you dislodge---for cleaning--use a power rodder--(and a pro to operate it?)
Rent a chain breaker to cut the iron----neat,five minute job---
Be sure the iron is properly secured before cutting---Falling iron drains can change your life forever.