Alexander Galkin wrote:

I need to replace large portion of main DWV stack. My main stack is composed
from two 4" cast iron Y fittings stacked one on another. There is then 4" by
3" cast iron reducer and then there is 3" copper stack pipe. All cast iron
fittings as well as main 3" copper stack pipe connected to cast iron reducer
are joined using bell end and lead. I need to remove all cast iron fittings
except one that enters my house from the street. I need then to cut 3"
copper stack pipe somewhere and replace all fittings and portion of copper
stack pipe with PVC pipe. I will use no-hub coupling to connect PVC pipe to
3" copper stack pipe. However how to connect PVC pipe to bell end of 4" cast
iron fitting that enters my house from the street? What's the proper way to
do this?

Consider the stronger Pro-Flex coupling for the PVC-to-Cu transition:
http://www.fernco.com/noframes/proflex.html

For entering the cast iron bell, use a rubber "Donut" (also Fernco).
Just slips in place; no lead req'd.

To remove the existing lead, use a long drill bit and
"swiss-cheese" the joint until you can pry the lead and oakum out.

Jim