Boss for plastic waste into cast iron 2.5" soil pipe

[phb10186]

I have a 30's house with the original hopper and 2.5" (I believe) cast iron waste down pipe servicing the bath and sink waste from the bathroom on the 1st floor.

I now need to run two new plastic wastes from the ground floor in to this cast iron down pipe.

I either remove the old cast iron and replace with plastic, or if possible, is there a snap on boss or similar available (or any other solution for that matter) for this cast iron smaller 2.5" waste?

 

[Fluffster]

Best bet is to replace it with plastic.

Pete

 

[Hugh Jaleak]

Best to replace as said, but bear in mind there are no fittings available to connect waste (of any size) to 2.5" (68mm) rainwater pipe.